I’ve been using Twitter for several years now. Here is how I use it.
Most of what I tweet is useful information, very little sales copy. That way people actually want to follow your tweets. Tweet about things that are useful, interesting or entertaining and people will start to follow you and re-tweet your tweets. After 40 or so tweets you can slip in sales copy.
Brand Your Business! As a business person you are on there to make money, not friends. I tweet at least once or twice a day, but I only spend about 10 min./week on Twitter.
Your business should have a blog and you should be posting to it at least several times a week. When you do, send out a tweet about your blog post and put a link back to the blog post, not your home page. That way you get a link to your blog post and your Twitter followers have a place to get more information on your tweet.