I try and only buy a book when I'm ready to start reading it, which is why I really like e-readers, because you can buy a book on the spot, even while laying in bed.

I used to spend lots of money buying books I might want to read "some day" and ended up with bookshelves full of books that I would probably never actually get around to reading.

Now, when I've finished one book, I scroll through my "want to read" lists, pick one, buy it, and start reading it immediately. Saves me money.