Wikipedia has a veritable "alphabet soup" of policies and guidelines. But all these policies and guidelines are elaborations on three key points.
Wikipedia is an encyclopedia created by the community through collaboration, and these three basic characteristics suggest three basic guiding principles for editors. Other principles, policies, and guidelines can be viewed as more elaborate formulations of these three simple points.
Wikipedia is a community, and editors ought to treat each other – and the encyclopedia itself – with a certain level of pleasant, polite respect. Yes, we're almost all anonymous; yes, things go wrong; yes, the system is crocked up sometimes. Don't be a jerk and don't call anyone a jerk. This is put more politely by our Civility policy, as well as other things like keeping your cool, assume good faith and no personal attacks. And remember unregistered editors are human too.