I'm really starting to understand why so many people rave about Twitter. It's a fantastic tool, and you can use it in so many different ways. Of course you've got to find people to follow for the whole thing to work. And hopefully those people will follow you back so you can interact with them by retweeting, replying and also direct messaging.
So, here are few things to look for when deciding who you're going to follow.
Firstly, obviously you should try and find people in your niche. You can do this by searching for keywords much as you would do with Google. I find lots of them by typing in "blogging tips" for example.
Once you've found some prominent users in your niche, then go to their lists. You'll often find more there.
Also, whether you're cruising lists or doing searches, then keep an eye out for people who are reasonably active, with a decent number of tweets already. And check to see if they've been active recently. And needless to say, they should be real people. You can usually tell if they're not by the sheer incoherence of their tweeting! And if they've got a photo of some celebrity, or a model's glamour shot on their main page, well, that's not a good sign.
Also, look for retweets and mentions of other tweeps in their streams. If these are present they are clearly interact with others. And chances are they'll be constantly looking for mentions made of them, and retweets of their tweets. So, they may well reciprocate if you mention or retweet them. That will of course get your profile seen by more and more people.
If you are hoping to promote yourself, and not just learn from others then I'd avoid tweeps who never mention or retweet others, even if they follow a lot of people. They are basically using Twitter as a kind of press release service, just tweeting their blog posts, articles and affiliate programs.
Also, see how many people they follow compared to their number of followers. If they are approximately equal, then this means they will often follow back.