I only have a semi-formalized technique for doing this.
Firstly, I followed some of the big Internet marketers, because I am interested in their stuff and they happen to be on Twitter.
Next, I followed a few people who have sales and marketing related blogs. Their blogs were good, so I followed those authors who have Twitter accounts, and most of them do. I often follow Twitter accounts mentioned by these same marketers.
I also followed a range of Chinese Twitterers after going to a Twitter meetup a while back. Much less of the follow madness with this crowd.
Almost all of the deliberate follows I’ve made recently are from blogs and links to other related blogs, mostly English blogs on Taiwan.
Then, for the constant stream of followers that build up. I check out their Twitter page. No avatar, no follow. Backgrounds with big $$$, or make money scheme, no follow. Only very old tweets, older than 1 month, no follow. Otherwise I decide on if the most recent tweets are interesting.
You can follow me too: @pumpkinslayer