Used wrong Twitter will drain your time away. Used right, it can be a useful tool.
Bear in mind, its not a tool to directly sell, rather a tool to get clickthroughs to where your offers exist.
1. Create an in-person event using twitter invites
2. Offer a free product relevant to your followers
3. Timing tweets to maximise views.
4. Drive traffic to your website through Twitter
5. Monitor what is being said about your brand