This is tiny list on how to be a good tweeter. Am I a good tweeter. You can make that out by following me @Mgmnt_secrets. ;) Anyways here's what I do. 1) Bothered by the 140 character restriction? Well, do not be. First type out whatever you want to. Then see how to reduce it to the 140 (or less; see next point) characters. The quality of your tweets will go up.
2) If you wish your tweets to be re-tweeted then you do not have 140 characters available with you. What is available to you is (140 - RT @your_tweet_id). In my case, it is 122 characters. I try to stick to this restriction.
3) Do not tweet to tell what you are doing at a mall or what are you eating for dinner. Your close friends may want to know that. But if you wish to build a good number of follower, use tweet-sense. Pick up a domain that interests you and tweet on that. Unless you are a celebrity - then you will have a HUGE following irrespective of what you tweet.
4) No typos. Use good grammar. And oh! avoid those silly acronyms please.
5) This is important: before pressing the send button, just pause. Does the message seem right? Are you proud of it? Yes? Then what are you waiting for? Send!