I bought The Eyre Affair simply on the basis of its cover and I have rarely enjoyed a book so much.

More often, though, I buy books that I've seen/heard reviews of, or that other people have recommended. And I do look for things that seem similar to things I know I like. I do a lot of re-reading, on the basis that it's safer to read something I know I already like than to risk something I might not. I need to work harder at changing this pattern..