How do you choose what book to read next?

The way I choose to read my next book usually falls down to whether it is available. If there is a book that I am dying to read and I can't find it at my school library or local book shop well then there is no point in just waiting for it. I usually choose a book by what I haven't read that is really popular for example City of Bones (I finally borrowed it so no fear) Sometimes I choose by the cover and blurb which I do quite often. I like to choose a mixture of books I have and haven't heard about so I get a bit of variety. 

So it falls down to: