Simply sending out regular, interesting tweets that your target market might find useful or informative is a good first step, but in order to get the best out of Twitter it's worth actively searching for relevant users and content rather than sitting back and waiting for it to come to you. Increasingly, sites like Twitter and Facebook are used for finding services. Sure, you could trust Google to find a mechanic nearby, but most of us would prefer a recommendation from a real person. Either we ask friends, family members, and colleagues if they know a good one or we turn to social media. Tweeting 'Anyone know a good cheap mechanic in San Diego?' is the work of a moment or two.
Monitoring Twitter traffic for queries relevant to your field and location is very easy. Tools like Monitter.com and TweetBeep can be set up to watch for them. A smart San Diego mechanic would get an email alerting them to an opportunity and if they're quick, they could pick up a valuable new customer with a simple, helpful reply. Industry-specific monitoring is also a great way to find sources of useful information and news that's relevant to your company.
Other Twitter monitoring tools can help a small business figure out the effectiveness of their engagement.