I don't tweet and refuse to join but business wise you use it like any other advertising tool except that it directly connects to your customers. Advertise that you are on Twitter asking your customers to follow you. Listen to other business commercials on either the radio or TV and you will notice them asking customers to follow them on Twitter. Start running special promotions for your Twitter followers, announcing them over twitter. You can also announce arrivals of new inventory, industry updates or maybe a "deal of the week".