Don't attach files or images, both because not everyone can read them, and because many people can't accept extremely long files. If you have a VERY large file, avoid sending it, but if you must, then send a short message first warning people that your following message is long and giving an approximate file size. Remember, one good scifaiku is a much better contribution than several bad ones. Stick to the Point. In all commentary and stories, be brief and to the point.
Minimalism is the key here.
Replying to Messages. However, be sure to keep the important context, especially the author of any poem you are quoting. Be sure to send replies only to the original author, unless you have something very important for the rest of the list to see, or if you have an additional poem to contribute that responds to the first. Don't get into flame wars. If an argument starts getting lengthy and only involving a few people, then you should be having it privately, not using the mailing list.