The Internet is a big place where lots of people intereact in a number of different ways. Unfortunately, it seems that a lot of these people forget that behind those words on their screen are other people. It seems to me that people should be treated with a certain level of respect that often seems to be missing.
Here are some examples of things that people do that bother me along with my suggestion for how to handle it.
I realize that it's unlikely that anyone will actually read this and change their ways, but I can always hope... I'll eventually work it up into a better format, but this is my thoughts as I think them.
If you reply to a letter or article, make sure you're adding something. A simple 'me too' letter is probably a waste of bandwidth. When you quote, try to quote only the parts to which you are replying. Remember that everyone on the list has already received a copy of the letter. When replying to someone on the list, don't bother cc'ing the letter to them. Odds are they'll get it from the list. Don't waste their time and your time and the bandwidth by sending them two copies.
Before you participate in a newsgroup or mailing list (or anything else, for that matter, read the FAQ. This will save you from a lot of embarrassment and potential flaming. On the flip side, if someone does something stupid or shows that they haven't read the FAQ, don't be rude to them. They may have a perfectly good reason for not having read the FAQ or just may have no idea that there is such a thing. The most common example of basic list ignorance I've seen is people sending list manager commands such as unsubscription requests to the list instead of to the list manager software. If someone does this, don't flame them. If you insist on flaming them, then don't flame them on the list. Everyone knows what they did and no one cares that it pissed you off. Try sending the person a letter pointing them to the FAQ or explaining to them where to send the request. If that's too much trouble, then don't waste your time by sending them a flame which will just make them feel bad or piss them off. Then everyone on the list will have to listen to the flames fly back and forth. Basically, if you don't have something nice to say, don't say anything at all.
Remember that when you post something, you're sending an example of your writing to a large number of people, possibly all over the world. Try to at least proofread it once. Look for major errors. If you're not very good at spelling, then look up words that you're not sure of. If you know you have trouble spelling, find a spelling dictionary. There are also dictionaries on the Internet, if you don't have an actual paper dictionary. People will take you a lot more seriously if it looks like you care about what you're saying.
Some classic examples of mistakes:
Personal Pet Peeve: Okay, this is just me, but I really dislike seeing posts with the following abbreviations or terms: r for are, u for you, d00d, kewl, and other lazy warez shorthand.