1. Do be easy to find
Choose a Twitter name close to your business name, and write a clear profile that explains what you do and where to find you. Use key words that people might be searching for: your neighborhood, your primary focus, and a link to your full website.
2. Don't shout
Using all caps is considered impolite. Consider grammar and spelling, too—even if it's casual, it's still important to be professional on Twitter.
3. Do provide timely info
Twitter is a great place to let people know about special menu items, limited-time discounts, or upcoming events. Give a peek behind the scenes: share a photo of a particularly beautiful new dish, or your rooftop herb garden, or your cooks in the kitchen. Invite your Twitter followers to get to know you a bit.
4. Don't repeat yourself
Don't tweet out your Facebook page every day—people can find that on their own. Don't tweet the same thing at a ton of people at best, it's boring, and at worst, it's plain annoying.
5. Do ask advice
Twitter is a great place for polling your customers: Do they like oysters? Do they like spicy drinks? Do they have a favorite coffee roaster? Get into conversations, and you might find out valuable information for your business.
6. Don't be aggressive
Though Twitter is a conversation, whatever you say is in writing. Don't say anything you wouldn't want reported in the local paper.
7. Do engage with your community
Be a friendly face, not an anonymous business. Share interesting articles, neighborhood news, and catch up with others in the same field. Twitter isn't just about self-promotion, it's about building bonds and giving a fuller picture of what your business is about. Retweet interesting tweets by others to support them. Use short links (many people like http://bit.ly/) so your posts can be retweeted. Aim for about half of your tweets to be non-self promotional. If you're going to share your twitter account among several employees, discuss what sort of "voice" your business account should have, and aim for a consistent tone.
8. Don't auto-tweet or auto-DM
Think twice before putting your Twitter account on automatic. Don't have it put your whole blog stream onto Twitter, and please, please don't send auto direct messages to new followers.
Thanks to Maggie Hoffman / Open Forum