After getting my hands a little dirtier I've come to find that it is critical to have a plan for your twitter. From the start you want to identify and evaluate the pros and cons of having too many followers, too few of followers, who your followers are, and where they're located.
I would start by imagining a list of my 5 ideal twitter followers (5 is just a suggestion) that can benefit my business. Flesh out the details, look for common themes throughout them so you know what kind of characteristics to do searches for.
With an idea in your head of your ideal 5 and a list of characteristics you can sign up for use www.twellow.com which is like a searchable twitter directory where you can follow people you would like to follow you back.
Josh is right, putting together a concentrated list can be just as much work as building one anywhere else, but having this list can help because your tweet stream from people you follow will give you a less fettered view of relevant tweets.
If you look at Wendy Patton's twitter account you can tell she autofollows and has quite a staggering number of followers. However, if you look at her list of followers her list is made up of the most random twitterers you could think of. So she maybe able to rank higher on directories and look like an authority based on twitter accounts, but one thing you can be sure of is that she isn't using twitter for her real estate deals with such an account.