Andrew has a good write up on how to read a business book.  It's good stuff that generally applies to other genres as well.

Books also tend to fit one of four flavors: prescriptive, descriptive, narrative, and fables. Prescriptives promise to particular solution: managing teams, motivating poor performers, making strategic decisions, finding a job, reaching your full potential, leading organizations, etc… and usually have some number of answers (5 secrets, 7 habits, 22 laws, etc…). Descriptives offer interesting explanations of what’s going on but no real actionable advice (e.g., The Tipping Point and The World is Flat). Narratives are the “great man” and “great woman” stories, usually auto-biographical, that explain how that one person was responsible for a company’s great performance (Who Say’s Elephants Can’t Dance). Finally, there are the fables, short books that offer a simple creamy insight inside a fluffy, allegorical, outside. Usually (and not surprisingly) food-related: like cheese, fish, chicken-soup. High-calorie and low-nutrition books, read them at your own peril. Know which kind of books you enjoy reading, when, and why.