Last year I decided to use a totally random method (after reading an interesting article linked here) to choose my next book among my huge reading list. Was weird and fun, since it let me read things I would have put off for a long time.
My reading list is also very long but I'm trying to mix on books that I think I'll really really enjoy with books that are good for me (that I'll still enjoy, but not as much).
one method that works extremely well for me is to pick a book based on Amazon's "what other customer's bought". I noticed that some of the best books I read appear in clusters that other customers/peers valued equally high