You want people to follow you. The best way to get someone to follow you is to follow them first. Or re-tweet or favorite something they've tweeted. Or do all three. I've said it before here in the Roo blog but let me repeat: sometimes the best way for people to think you're interesting is if you find them interesting first. Following, re-tweeting, and favoriting tweets is one way to signal such interest.
But that's only step one. People do not spend much time deciding who to follow back. There's a considerable body of research in both traditional marketing and online marketing about the very, very small window of opportunity you have to get someone's attention.