1) Phrase the subject title as a question. If you can't put a ? at the end, it's not a question!
Don't name your question "2 questions" or "I have a problem." Make it relevant to the information you are seeking. This will help other users searching the forums with similar questions.
Similarly, don't add "Urgent", "Important", or "Emergency" to your title. Everybody's on equal footing around here, and such labels may be a turn off to others.
2) One question per topic.
Unless the questions are related. In other words, don't ask a question about two completely unrelated things, like the Sound Editor and the Collision Groups Page. If you find yourself using "also", chances are good that the topics are unrelated. This also helps other users when searching for answers to the same problem, because they can identify the information contained in a specific post based on the topic.
3) Be specific.
Tell us what you're trying to achieve rather than having us guess what your intentions are. Be detailed - more information is better than not having enough. Describe any issues or errors as completely as possible (within your understanding of them) and it will reduce the number of questions other users will have to ask of you in order to answer your question.
4) Mark your questions as answered.
Edit your original post and change the Subject line to include [Solved] once the issue has been resolved. Again, this relates to the other forum users being able to find answers to their own, similar questions by picking out forum threads that have been successfully resolved. Additionally, if your question is answered somewhere outside of the forum (such as by yourself, IRC, email, Google, etc), it's helpful to other users to post your answer here.
Finally, please don't hesitate to do forum searches before creating a new post. Thanks!
Original post credit goes to Jon.