I dont market my business per say with Twitter. A common misconception are the people that create to blast advertisements about their business. Those types are worthless and never really see the benefit of Twitter.
On Twitter, you are in basic conversations with people. First, share what drives you or what you have to offer the community. As people around you gather you skills and abilities they may come your way. I every so often talk about something I am working on, but this is very rare.
I use Twitter much more to help people. They in turn know, I am knowledgeable and when they have needs they will come my way. Its sort of creating a word of mouth recommendation.