The art of picking a new book to read

It's very hard for me to start on a new book. Choosing which book to read next, can take me hours. I will go through different phases; first, happily scanning the bookshelve, choosing whatever catches my eye. I will then read the first few pages, until I suddenly realize that I've chosen the wrong book! It's wrong, I can't read this now! I will put it back in it's place. Next, I'll choose one of the books I bought ages ago, but still haven't read. It sits there, pricking my bad conscience. I'll take it out, read the blurbs, count the pages, read the review extracts hailing it, I'll put it back, thinking 'next time'. Often, I read thematically, this is very advantageous for picking a new book. Recently I've read the great sci-fi classics, this narrows the list down drastically. Sometimes, I've just read a very easy and light popular book, then I'll want a more heavy 'literary' book, like a classic, and vice-versa. Often I just choose a thin book, that way, picking wrongly, won't have so big an effect.