When replying to a post, check to see if someone else has already said what you want to say. Supporting opinions are good, but only if they introduce a new idea or make another point. When replying to a post, refresh people's memories by including part of the post to which you are replying. Remember, anything worth responding to is better when taken out of context. Extract only those phrases that prove your point or make the original poster look stupid.
Some posts are better off being replied to directly, rather than being sent to the entire network.
Always check the reply address before replying. Don't bother to ascertain where your reply is going. This makes for lively exchanges and a great deal of amusement for the rest of the list. If a personal slam against someone accidentally gets sent to the list, you can just try to deny that you ever sent it. Also, be sure to send your subscribe and unsubscribe requests to the list.