There are generally two types of parenting books:
- Those that strive to be objectively informative
- Those that advocate a particular style or method that the author subjectively feels is useful.
Those of the first type can usually be judged by the credentials of the authors (e.g. The American Academy of Pediatrics), although not always (the authors of the "What to Expect" series don't have impressive credentials iirc, but their books are very popular).
The second type seems much more common on the marketplace these days, and provides a much wider range of reactions (from "OMG! How can anyone survive without this?!?" to "What idiot decided that publishing this garbage was a good idea?!?"). Therefore, choosing from the selection of subjective books becomes a trickier decision.
When choosing subjective books, first and foremost you should review the general premise or philosophy of the book before you purchase it. If you don't agree with the author's (or authors') justification as to why their method/style/advice is "the way to go", then chances are you will find very little worthwhile information in the book.
Always remember that any book with subjective advice (no matter how much the author tries to present it as objective fact... and they almost always will do just that, btw!), you are under no obligation to agree with 100% of the author's opinions! Making sure that you at least marginally agree with the basic premise, though, gives you a much better chance of finding at least some advice that you will find useful and applicable.