I have a reserve of books that I intend to read left over from my days working in a used book store. Used book stores, ultimately, are the primary source of my books. I read both fiction and non-fiction. My criteria for purchasing a book is that it looks interesting to me. What you are left with is eclecticism.
My non-fiction tastes have narrowed to history first and science second. I'm not just reading "Rise and Fall of the Third Reich" over and over again, however. Sure, war can be interesting, but there is much more to human civilization than its occasional fits of self-destruction. I try to keep things a bit more broad. In general I'm guided by a desire to know more about the things I don't know anything about.
My fiction tastes generally see me reading science fiction and fantasy. If you are unwilling to accept these as literature, than you and my blog are probably not going to get along. Not to say that some of the books I read aren't fluff, (this goes for non-fiction as well). God forbid I ever enjoy myself.
I move from book to book guided simply by what I feel like picking up next. Often this is influenced by some little idea the previous book got in my head. In fact this thread of thought might yet make for an interesting post some day.
The early days of this blog will give off the impression that I am a reading machine. I am not. I simply have a backlog of books to review. Given my goal of making this place an "archive" I can't imagine a problem.