These 3 things are important to know about Twitter.
1. Tweets between 3pm and 6pm will be very effective. I find that if I tweet on other times I don't get the same results.
2. Ask your twitter followers to retweet you. If you don't ask not many will ever retweet you. In fact if I ask I noticed an increase by 4x.
3. For every 100 twitter users I follow I will get about 25 to 30 followers.