Posting ones from the other thread that weren't here:
Observe the rules of anything you post on. If profane words and visuals with nudity are forbidden, do not use them.
In an internet discussion, read the entire thread before posting. It is tiresome to participants to repeat themselves in response to you and tiresome to subsequent readers to see the same answers repeated by others.
Stay on topic.
Even if the forum/site doesn't have rules about this, please limit the size of your sig photos or graphics. It is annoying to other readers to have to scroll through two or more screen lengths to get to the bottom of your post, especially if the text is only a single line or word.
When forwarding anything please remove all the other headers in between. Some people's e-mail programs create nested attachments which can become 20 or more layers deep, so it is rude to make them open the item 20 or more times to get to the cartoon or joke you were intending to forward. It should also be considered rude to forward people's e-mail addresses to strangers.