Make it easy for people to find your business on Twitter by adding your Twitter username to all of your business materials.
For example, you should give your Twitter username in these locations:
Your website (with a link)
Your email signature (with a link)
Your email newsletter (with a link)
Your business cards
Signs posted in your business
Paperwork you give customers (receipts, invoices, statements, etc.)
Menus and product information sheets.