Before posting, have a read through
these.
1. Observe how respected members post on the forums, and learn a few things from them.
2. Make sure your post makes sense.
3. Make sure your reply is related to the topic it's posted on.
4. Think before you post, will this possibly offend anyone? If so you probably shouldn't post it.
5. Don't post on threads where their last reply is over a month old, or you will be banned for Necroposting.
6. Don't be a kissass in public, people really don't appreciate it.
7. Do you honestly think anyone will give a shit about your post? If not, don't post it - or prepare for hate.
8. It's fine to post your opinion, but make sure it's appropriate and respectful - I'd advise to stay clear on posting your opinon on contreversial topics.
This guide pretty much sums it up for you.