Lawful Good Alignment

Lawful Good characters always do the right thing, as expected by their social standard. They always follow the rules, tell the truth and help people out. They like order, trust and believe in people in positions of power, and they aim to be an upstanding citizen.
Lawful Good characters believe in societal rules because they benefit everyone. If everyone followed did whatever they wanted there would be chaos and people would end up hurting each other. Laws ensure that the good is maintained for the majority of the people.
Justice is really important to Lawful Good characters. If someone doesn’t follow the rules, they should be dealt with by the authority system. They are angry when people get away with breaking the rules. They also believe that good behavior and good deeds will be rewarded either socially or within the system.
A Lawful Good character holds themselves to the same standards that they hold everyone else. They very rarely, if ever, break the rules. If they do break the rules they will feel very uncomfortable doing so and will be compelled by a greater good. They might also do so unknowingly because they are tricked or lack knowledge in the particular matter. In either case, they are likely to present themselves for judgment after the fact. They will believe that the system will take into account the context of the actions and judge them accordingly.
If a Lawful Good character encounters a culture with a different belief to their own, they will not necessarily try to push their own values onto the people in that society. But it depends on what the laws are. If the laws are at odds with their alignment, the character might encourage citizens to ignore them, or even try to change the laws themselves. But it is very unlikely that they would remain within a culture that greatly opposed their belief system without trying to create change within that system.
There will be times when the Lawful aspect and the Good aspect of their character disagree. For example, taking down the evil leader but allowing innocent civilians to be hurt in the process would side on Law over Good. Saving the civilians but letting the bad guy get away would side with Good over Law. If a Lawful Good character regularly chooses to take the Lawful decision over the Good decision and innocent people are negatively affected as a consequence, they can find themselves aligning more closely with Lawful Neutral or even Lawful Evil. In general, the lawful good character will side with good when these are in conflict with the idea that the evil leader can be caught in the future.

Lawful Good. (LG) creatures can be counted on to do the right thing as expected by society. Gold dragons and paladins are typically lawful good. -5e Basic Rules, Chapter 4: Personality and Background