You look for stuff you already know and then browse the users library, if they have stuff you already like then anything you don't recognize is probably also to your taste, especially if they're sharing a smaller collection.

Perhaps I'm lucky that there's not much I don't like because it's a similar strategy I used to use for traditional media, buy something I like and get something out of the bargain bin I've never heard of and 9/10 it was pure gold.