You basically have two options:
1) Pick a niche and start following / unfollowing. Build up a big follower list and start advertising. More of a long term strategy if you can be bothered, you won't make immediate cash out of this and it's more work than option
2) Pick a niche, scrape some follower lists and start hammering out @replies. Your accounts will get banned in short order but you should make some money out of them.
You could also: sell them, there are always people looking for Twitter accounts; or add a few more followers and use them just for SE indexing purposes and not post commercial links.