Twitter may or may not be here to stay, but I can tell you that it works very well for some clients! Be sure to tweet regularly (at least once a day); tweets that are too far apart will cause your potential clients and customers to lose interest. Include a special offer from time to time (something that’s only available on Twitter!)
Follow the people in your industry, your potential clients, experts in your field, and magazines or publications relating to your product or service. When you see something interesting, be sure to retweet! And by all means reply to someone with a comment if what they tweet is of interest to you.