If you are replying to a message be sure to include the text of the original message which you are replying to. Keep in mind that the Internet is international, words and humor can be perceived differently by different cultures. When responding to a post, keep the subject line the same, so that it will appear in the same thread. Cross posting to multiple lists is often prohibited. Expect a delay when posting to moderated forums, this means that each post must be approved before its posting.
Anonymous posts are unaccepted in many newsgroups.
Also keep in mind that anything goes on unmoderated usenet, Moderated forums tend to have more decorum.