Hephaestus's Guide to Thinking Sideways

Introduction

As I have watched the questions that are frequently asked about worldbuilding on the WorldAnvil server, I've noticed that many of them share a common theme of I have this idea, but it's not finished and I really don't think that it will work anyway. Most of the time, when the idea is presented, it's not bad. It's not usable in its current state, but there is nothing wrong with the underlying concept.
While I am very happy to assist anyone in any reasonable way that I can, I thought that it might be best to capture some of my key thoughts on the subject of worldbuilding in a single article, so that I didn't keep repeating the same advice and clogging the threads. The best way that I could think of was to provide some examples from Sama, my current world, and perhaps some from early worlds that I've run (successfully and unsuccessfully) in the past.
As always, your mileage may vary. It's your world and your vision, do things your own way. If you disagree, great! Write up your own thoughts and share them. Everyone will benefit (including me). If you do agree, feel free to point people to this article as a starting point.

The Source of Ideas

Ideas are everywhere. You trip over a hundred ideas a day that could be used for worldbuilding. It doesn't matter whether you're into fantasy, horror, science-fiction, or something else. The ideas are all around you.
You're just not looking in the right place.
The problem is that great worldbuilding is great story-telling. The two are intrinsically related. If you can spin a story, you're building a world as you go, even if the story is a completely factual account of what happened.
For example, in my city, there is a hazardous waste drop-off site, but if you want to get rid of cans of old latex house paint, you can't bring them to the site. Instead, they need to be opened up, allowed to dry, and then put in with the rest of your usual trash. Pretty simple, eh?
Except that I need to clean my house now, because I'm moving. And I've got roughly sixteen gallon-sized cans of old paint, most about a quarter full. Now, the trash people helpfully suggest mixing kitty litter in with the paint to thicken it, which I did. Unfortunately, this week it's -9°F (-24°C) here. (Why do you think I'm moving?) Thanks to Prof. Svante Arrhenius, I know that chemical reactions proceed at a rate that depends upon the absolute temperature. Unfortunately, the difference between room temperature and the current temperature in my garage is giving the "watching paint dry" new meaning. Those fifty degrees make a big difference in an exponential equation and what seemed eternal before becomes profoundly so.
In the wee hours of the morning, I was frantically opening paint cans, dumping kitty litter, and stirring. Eventually twelve of the sixteen cans became gelatinous enough that I was willing to bet that my neighbor's yard would not look like a rainbow snow cone when the truck flung my trash into its bowels.
The other four will set (with luck) by next week.
That was a story. In order to tell it, I had to build a vision of a world and share it with you. I would hope that as you read, you imagined me, in a cold garage, my breath hanging in the air, desperately stirring cans of paint like some demented witch. When I mentioned the truck flinging the paint and creating a rainbow snow cone I hope that you saw that in your mind. (If you've never seen a snow cone look here.)
So what? Where is the worldbuilding inspiration in that?
What if, in your world, you decide that magical potions must be made very slowly. If you mix them too quickly, BOOM! Because your world is pre-industrial, you can't make potions in the tropics. In the temperate climes, you can only make them in winter. And the most powerful potions of all can only be made in dead of a polar winter, out on the ice cap.
Now you have a reason for adventures to far-off lands. There is the opportunity for urgency as a wizard hires the characters to fetch a rare ingredient "before the snow falls!" You have an excuse to put some magical places in hard-to-reach areas and to limit the use of powerful magics in other places.
And all because of a can of paint.

Why Are You Stuck?

I don't know you. The chances that we've ever met are microscopic. Still, if you are here on this site and you're trying to build a world, I'm willing to bet that you have a pretty active imagination.
So why are you stuck?
Another quick real-world example and then I'll show how it works in worldbuilding:
Years ago, I lived in Texas and we had a freak ice storm. It wasn't all that bad, but the city wasn't designed or equipped for it, so everything shut down. I happen to have a lot of experience with driving on ice, so I went about my business as normal.
Until I came to a railroad crossing.
The road had a small rise up to the level of the tracks. We're talking three feet (one meter). That's all. There was an older lady in a fur coat, driving a Cadillac that was about the size of an aircraft carrier in front of me. When she got to the rise, she tried to drive up the hill very slowly. And at a certain point, the wheels would spin futilely and she would slip back. I watched her try three times before getting out of my car and walking forward to tap on her window.
"Ma'am. If you got up speed here on the flat, you could just coast over the hill."
She gave me the look of death and made two more useless passes, each time sliding back to where I stood. After the second pass, I asked if I could try with my car. She gritted her teeth, but agreed.
I got in, went around her, picked up just enough speed so that I could lift off the gas and I coasted to the top with just enough momentum to get across the tracks. I then went down the other side without picking up too much speed and made it to the stoplight. I looked in my mirror and sure enough, there was the Cadillac on the slope, wheels helplessly spinning.
She was stuck because she could only think about moving straight ahead. Other options were out of bounds.

Example of Building a World

So, now let me tell you about my world. To start with, I like history a lot. I also read a lot. Perhaps not coincidentally, I happen to read a lot of history. The thing is, an awful lot of what I read is pretty obscure. What's the fun in knowing what everyone else knows, right? How bad is my reading habit? My wife bought me bookmarks that say, "Yes, I'm actually reading this." (I do have a friend who's worse, but he's not married, so he doesn't get this kind of abuse.)
And here is where the idea for my world comes in. Let's say that we have a sufficiently powerful supernatural being who can travel through time and space, and what's more, can alter time and space. We'll call this being Fred. (In honor of my friend.) Now Fred comes upon the Earth one day in his wanderings and he thinks it looks interesting. So he whizzes back and forth through history and what does he discover?
The Earth has had this wonderful collection of great empires.
A lot of empires. Unless you have a doctorate in world history, I'd be willing to bet that there are a whole lot more empires than you've ever heard of. And all of these empires have similarities. And they have their differences. But which one is the coolest? If only you were a nearly infinitely powerful supernatural being with the ability to move in time and space and alter the nature of time and space.
Oh yeah. You are. Your name is Fred.
So you create a bubble universe where you can control the laws of physics (more on this in a bit). You scoop up some generally suitable stars without populated planets, pick a likely candidate, do some world sculpting and terraforming, and drop some generally earth-like flora and fauna upon it, perhaps with a few minor tweaks.
And now you populate the world by zipping back and forth in human history, stealing people from each era and bringing them to your new world. You erase their memories of personal events and arrange for them to wake up, simultaneously, in the new world. At hand is food and water and you've given them suitable places to build whatever they want.
To make it fair, you've limited yourself to pre-renaissance iron age empires. So the Babylonians and Macedonians don't make the cut. They'd be wiped out by the first iron-wielding people they came across. Neither do the British, Spanish, or Dutch colonial empires. Without firearms, they'd be wiped out by their first encounters, too. Ditto the Americans, Soviets, and Napoleon. All great empires, but perhaps for another world.
And to level the field a bit and make things more even, you've made a few adjustments. First, a few of the civilizations are dumped into ecological niches that are a bit different than they knew before. Why? Because either they were handicapped by the niche on Earth, or because they got lucky with their place on Earth. By changing it up, you'll make it more fair.
Second, you'll introduce some constraints on the playing field. There are no fossil fuels available. Instead, the trees grow really fast. This means that you can whack away at your local forest and have all the lumber, firewood, and charcoal that you can use. But no one gets coal or petroleum. You also make certain that every empire has access to raw materials like ores, etc.
Third, you've thrown in a few wildcards. The biggest of these is that you give your bubble universe a new physical field called "Ka". Ka is something like the electromagnetic force, except that it can be manipulated by the mental power of intelligent life. Ka is not evenly distributed, there are nodes where it is stronger. It has odd effects on living things that grow in high-ka regions. It can be stored in gemstones and crystals, but not in living things.
And it accelerates chemical reactions. This is part of its effect on living things, but it also keeps gunpowder out of the world. See, there are ley-lines that connect ka nodes and these lines are constantly snapping into new configurations in order to find the lowest energy state (did I mention that I'm a physicist by training?). The problem is that when you cross a ley line, or one snaps past you, it accelerates those chemical reactions. Your fire flares up suddenly. Or that keg of gunpowder suddenly decides to spontaneously combust. All at once.
That problem is solved.
So, I create lots of maps, carefully design the terrain, assign empires, write rules, think about geopolitics and I'm ready to run a game and I realize something very, very important.
It's going to suck.
Big time.

Where It Went Wrong and Fixes, Take 1

The world is a very, very big place. Unless you happen to live in one of a very few places that are very strategically located, I would be willing to bet that you could not walk from your house to the capital of the next of the next nearest historical empire in six month's worth of walking. And I mean daily hiking. Not real migration type walking where you will need to settle down and grow crops every now and again.
Even given roughly 1500 years of global empires, when you spread them out around the world, it's a pretty sparse map. After all, medieval civilizations don't build megalopolises.
This means that either my campaign is going to take place in one of these civilizations and the other thirty-four were a complete waste of time, or everyone will spend their time trekking around through mostly empty wilderness. Lots and lots of random encounters with wild animals and the occasional party of inept bandits.
Well, that's going to last for one, maybe two sessions. It's not even a particularly good adventure, let alone a campaign. What can I do to fix it?

Throw in Some Other Races

Realization: It's a fantasy world. Players are going to want some fantasy.
So, unless I get really lucky and put together a group of people who are insanely interested in gaming out historical empires (and they're out there), most people are going to be very disappointed to discover that there are only humans on this world.
Clever idea: Fred has the ability to alter time and space to his liking, right? So in the past, he scooped up various branches of the human family tree, transported them to suitable worlds, did a little genetic modification. (GMOs — fortunately I'm not gaming in the EU.) Bingo, I now have elves, dwarves, and giants.
No hobbits. Hobbits are the ewoks of fantasy. They were just thrown in to improve the marketing opportunities.
These can be dropped in to fill the empty spaces of the map. They each have an ecological niche to call their own. Life is good. If you wander around a bit, you'll bump into something. And, because I'm twisted and I don't like my players to know everything about the world before they start, my elves, dwarves, and giants aren't typical. For example, the dwarves don't live underground. Instead, they live like most people in high mountain regions do: they're herders and they move their herds from high meadows in the summer to lower meadows in the winter.
Huzzah! Problems solved! Let's game.
Except I need some history. If everything starts the day after everyone wakes up, I've recreated Phillip Jose Farmer's Riverworld, but that's not what I want. I don't want my characters trying to create civilizations. There's not enough time and enough players who would be interested to get anywhere.
Besides, if you have history, there are ruins to explore, legends to provide plots, artifacts of power and value, and all that good stuff. So I start to map out the history of my world. I want it to be long. I want there to have been rises and falls of great civilizations. I want parts that have been destroyed and rebuilt again and again.
But when I start to map out seven thousand years of history. I realize something very, very important.
It's going to suck.
Big time.

Where It Went Wrong and Fixes, Take 2

Seven thousand years is a lot of history. And, as any historian will tell you, history tends to consist of the same damn thing happening over and over again. So, even if every era looks like the Roman Empire, I'm looking at about four and half runs through the same show.
Now, this might not matter as much to the players. After all, they won't see a lot of this. But it will matter to me. And one of the things that I learned long ago about running a campaign is that if the gamemaster doesn't really have an overwhelming passion for his/her world, no one else will, either. And I sure as hell wasn't going to care about a world that was making the fifth pass through the same history.

Thinking Sideways

This is where I realized that I had been trying to climb that hill over and over again using the same method and getting the same results. If I was going to get over the railroad tracks, I needed to look at the problem from a different angle.
I needed to think sideways.
So, what if I changed it up a bit and let the inhabitants of my world have a chance to break some of the rules? What if I said that at some point in history, a group of powerful ka weavers gets strong enough to actually break through the bubble universe wall to another bubble, at least for a short period?
What if they were involved in a massive war against each other and decided to augment their armies by bringing in a new wave of races? Since they're not nearly omnipotent, like Fred, they can't wipe the memories of the people they snatch. Since they're not in it for the sake of curiosity, they don't look for well-adjusted species and they don't take care not to step on other races' ecological niches. In short, what if they behaved like typically power-hungry people who will stop at nothing to get what they want?
Ahhhh. Now there is an idea.
And so orcs, goblins, hobgoblins, and kobolds entered my world. Not with a whimper, but with a bang. The next time through the history loop certainly would look different than the first. For one thing, even after the initial wars finished up, bringing civilization to a crashing halt, there would still be competition for the same resources. And now I had four more races to play with in my own peculiar way.
It still wasn't enough to get me through seven thousand years, though. I needed one more pass through the loop.
I won't tell you how I solved this one. There are two reasons: the first is that it's not completely solved, yet. I mean that I know what happened, but I haven't figured out all of the implications of such a world-altering event. I'm still working it through.
The second reason is that this happened much more recently. The characters (and the players) are going to have much less knowledge about what it means. As a result, I don't want to spoil it here.
And this time, when I started to run through possible plot lines I realized something very, very important.
It isn't going to suck.
But it still isn't quite right.

Really Thinking Sideways

I mentioned that I was moving. This means that, among other things, I needed to clean my oven and stove. Completely, top to bottom. We've lived in this house for twelve years and two kids learned to cook on that stove. Cleaning it was an eldritch horror right out of Lovecraft. The more I cleaned the more I discovered unspeakable things that man was not meant to know.
This gives you an opportunity to think. Trust me, if you are ever faced with such a situation, you'll desperately want to think of something else.
And while I was inhaling fumes from chemicals that had labels warning that they should only be used while wearing biohazard suits in ventilation conditions resembling a full gale, I really got to thinking sideways.
You see, I had decided that my orcs were going to occupy the same forest niche that my elves did. Not exactly the same one, because the two races are different, both physically and mentally. But, still close enough that they would inevitably rub on each other.
Since my orcs were newer to my world both in world time and real time, I hadn't thought them through as much as I had the elves. I knew that they wouldn't be mindless brutes. There's no fun in that. Instead, they would have their own culture and it would be just as rich as the elves or humans. But what would that culture look like?
And it came to me.
I washed my hands and dried them. Then I poured myself a small glass of inspiration (it was very late at night by this point). And I sat at the computer and began to type.
One of my civilizations is the Iroquois Confederacy. For those of you who aren't American (and for those Americans who learned their history in school), the Iroquois Confederacy was the most powerful nation state north of the Incas for the period in which Europeans colonized the Americas. They were truly an empire, consisting of six nations, plus conquered peoples and they lasted for nearly seven hundred years.
(See what I mean about there being all sorts of empires that you probably haven't heard of?)
What's more, the Iroquois, or Haudenosaunee, had their act together. These people had a legal system, elective government, an effective military, and made advances in agriculture and medicine. If they had had horses, they probably would have dominated an area the size of the Roman Empire.
They were going to be one of the cooler parts of my world. They ... occupied ... a large area ... that was ... partially forest ... and partially grassland ........
It must have been the fumes. Because it all became clear.
Orcs would live in tribes that formed nations that joined together into powerful federations. I would give them the area that I had set aside for the Iroquois, as well as a couple of other similar places around the world. Now I would have a really cool and totally unique culture for characters to have to deal with. The plotlines swirled in my head (or maybe it was the bourbon). Perhaps I could do this with the other races, too.
And I realized something very, very important.
It isn't going to suck. At all.

Conclusion

This has gone on for a lot longer than I had thought that it would. I've covered a lot of ground on the subject of worldbuilding and given you an extended (quite possibly too extended) example of how to beat an idea into a viable concept for a world. I hope that helps you as you begin to develop your world, whether here on the WorldAnvil or in spiral notebooks and three-ring binders.
Now, if you'll excuse me, I've got a ton of packing to complete.

Disclaimers

1) This article is free. You get what you paid for.
2) No, I won't share my world with you. At least not yet. This may change as I get farther along.
3) The opinions expressed here are my own and do not reflect those of my employer, the WorldAnvil team, anyone with common sense, or (all the gods know) my spouse.
4) This material is licensed under the Creative Commons BY-SA License. That means if you use any of this in your own work, you must give me credit and you must use the same license.

TL;DR

I'll summarize everything into four rules that will be completely confusing when taken out of context.

Hephaestus's First Rule of Worldbuilding

Worldbuilding is nothing more than storytelling. If you can tell a story, you can build a world.

Hephaestus's Second Rule of Worldbuilding

Ideas are everywhere. You're just not seeing them, because you're not looking.

Hephaestus's Third Rule of World Building

When you build a world, think about how your characters will interact with it.

Hephaestus's Fourth Rule of World Building

If you don't care passionately about your world, don't expect your readers/players to.