Here are a few general things to keep in mind:
Be polite
Take your time and think it through
Good spelling and grammar help a lot!
Do not curse
Don't use all capital letters - people will think you're "yelling"
If it helps illustrate your point, include an image
Don't just say "I don't know" or "If you do a search, you can find the answer" - It just isn't a very helpful answer, and often times people are asking here because they've already tried to use a search engine and still couldn't find what they wanted.
Cite your sources - people are more likely to believe you if you can back up what you say. The best way to cite a source is to paste the link right into your post
When giving a link to a page with the answer, also provide a summary the answer. This way, if the site you're linking to goes down, people on Answerbag will still get a good answer, not just a broken link
Stick to the facts - if you can cite specific facts, events, or your experience, your answer will appear more authoritative
Do not belittle the questioner. Everyone deserves an answer
"OK I admit I did not adher to all those conditions in the past, but I will absolutely do so in the future."
alan