You can find people using Twitter people directories such as We Follow (google it) which group Twitter users according to the content of their feeds... so then you are only following people related to your niche
hi i offer such services to webmasters offering non targetted and targetted followers http://get-lots-of-twitter-followers.com/
I've had good luck by focusing on my geographical area. Then again, my blog content is quite focused on my area of the world. Still, I think p-eople might follow you (assuming excellent content) if they are physically nearby.
A great way to increase twitter followers is to send retweets. This is a powerful tip because the more people retweet your link, the more will visit your profile and follow it.