Here are links to two services I’ve begun using to help understand and manage the followers associated with my Twitter accounts. They help you to analyse both who is following you and the accounts that you are following. This means you can then do various housekeeping tasks such as making sure you are following back those following you or unfollowing inactive accounts.
This is a simple service that divides your Twitter connections into three types; following: those you are following but who don’t follow you, fans: those who follow you that you don’t follow back, and friends: those with whom you have a mutual connection. It also works with Instagram and Tumblr.
This is the more advanced service and breaks you Twitter connections down using several different measurements. For example it looks at the ratio of followers to followed for each connection or can tell you who are the most ‘talkative’ accounts. It can also identify fake or spam accounts. I’ve found particularly useful the list of inactive accounts it provides.
Both services are free but have premium options for power users.