...is to begin with the question, "Have you read X?"
If it's a famous book, the person who hasn't read it may be put off by your presumption. If it's obscure, you may generate some interest, but the wrong tone can still make you come across as a pretentious ass.
A better way is simply to say,"I happened to be reading X the other day (or whenever) and I was thinking (fill in your thiught). What do you think of my idea (observation, insight, whatever)?" This or some variation of it will give people a chance to respond to you and your thought rather than putting them on the spot. They can talk about the book if they've read it, but they can also defer to you without feeling stupid.