It’s hard to clean up your list of twitter followers and otherwise manage your twitter account: alot of tools that used to do that have closed up shop or now longer work. One that does still work is ManageFlitter.
I used it last night to delete over 100 people that I followed. I had around 540, and I seemed to be having problems with twitter. This tool helped me find inactive accounts and other people that I follow that don’t follow me, and made it easy to delete them. I highly recommend it.