You wouldn’t go to a party and ask people to leave with you to go to your store, right?
Yet I see businesses join Twitter all the time and do nothing but promote their business.
Yes, you CAN use things like contests, specials, exclusive content (particularly effective on Twitter), events, etc. to drive people to your business, but first you have to build a positive reputation, and connect with some of the communities on Twitter.
What this means is very simple: You have to network first.
Make connections, be helpful, share interesting information, and over time add information about your business bit by bit.
Businesses too often get confused about what is really a very simple formula:
Get to know people first, share information about your business second.