I generally just try to choose whatever route that seems natural to me versus trying to be pure good or evil. In most games, I'll end up being the good character but in some games, I'll be the bad character. I think that the morality system in a lot of games is often poorly designed. Some games try to treat morality as if it's based purely reputation instead which isn't logical because because your reputation wouldn't be affected if no one witnesses the good or bad acts. Someone being a good person or not isn't a matter of public opinion.
A good person is generally selfless and the act of helping someone is the reward itself. They shouldn't be doing quests or favors for others purely for rewards. They usually have good reputations by default. Sometimes, their actions can hurt others just as much as it helps.
A bad or evil person is ultimately a selfish person and do what benefits them the most versus helping others for no reason. It's usually the easier and most rewarding path. They can have good or bad reputation depending on how their actions affects others and how open they are with their bad acts. Sometimes, their actions can have positive effects on others.
