I have about 350 and have been active for just over 1 year. The majority of them are follow-backs from having gone fishing for them by searching for key phrases. It has been a slow going process, since Christmas I have been more diligent and have increased my followers by almost 100. It's my goal to have more interaction with others than acquire a forest of trees.
I have few contacts. It is hard to find right sentences to fish people as it is not my mother tongue language.
The best is to be in personal contact. The communication is not technologies ( facebook, net, email, etc...) but relationship.
I'm a photographer and Web / SEO consultant in Brighton on the South Coast of England. I started using twitter as a family thing and have been picking up followers since I started tweeting about stuff in general. I notice that if I tweet about certain subjects I get more followers immediately. Things like SEO or Business Coaching.