Civility is required at all times; rudeness will not be tolerated.
Treat others with the same respect you’d want them to treat you. We’re all here to learn together. Be tolerant of others who may not know everything you know. Bring your sense of humor.
Above all, be honest. If you see misinformation, vote it down. Add comments indicating what, specifically, is wrong. Provide better answers of your own. Best of all — edit and improve the existing questions and answers!
May I promote products or websites I am affiliated with here?
Be careful, because the community frowns on overt self-promotion and tends to vote it down and flag it as spam. Post good, relevant answers, and if some (but not all) happen to be about your product or website, so be it. However, you must disclose your affiliation in your answers.
If a huge percentage of your posts include a mention of your product or website, you're probably here for the wrong reasons.
I think similar norms applies to promoting a view or belief over the site. It is fine to ask and answer your own question but this works only when you genuinely had a question in the first place. If your goal is to promote a particular belief or sect or challenging other sects or beliefs and you are using the question format to that end then the post is not a real question and should be closed as such. Using the question format to post your opinion/beliefs and promote them and conceal the fact that you didn't have a question is not honest.
What should be done in this cases is to try to edit the question and improve it to address the issue if it is possible (which is usually the case) and normally users learn how to write better questions through this process. However from time to time we will have repeated offenders who will insist on their behavior, in such cases a more serious action maybe needed. In these cases inform the moderators with flagging the question. A moderator comment usually has more weight for users and most users will comply with it. Still some users will not. The moderator can raise the issue on the meta and take more serious action if needed (like banning).
(It is good to have meta discussions or blog.SO/MSO posts to link and base the decisions/comments on so the user understand that the point being made is not just one user or one moderator but a policy and the community in general disapproves the behavior.)