Assume good faith is a fundamental principle and a core policy in every community. As we allow anyone to edit, it follows that we assume that most people who work on the project are trying to help it, not hurt it. If this weren't true, a wiki project would be doomed from the beginning.
What constitutes Good Faith? According to MeatBallWiki:
* No intention of malice.
* People trying their best to do their best.
* People trying their best to do their best for the greater good of the community.
* Friendliness, honesty, caring.
So, when you can reasonably assume that something is a mistake, correct it without just reverting it or labeling it as vandalism. When you disagree with someone, remember that they probably believe that they are helping the project. Consider using talk pages to explain yourself, and give others the opportunity to do the same. This can avoid misunderstandings and prevent problems from escalating.
Assuming good faith is about intentions, not actions. Well-meaning people make mistakes, and you should correct them when they do. What you should not do is act like their mistake was deliberate. Correct, but don't scold. There will be people on the wiki you disagree with. Even if they're wrong, that doesn't mean they're trying to wreck your wiki. Just try to be somewhat civil.