I heartily second Icon's recommendation to constantly be re-reading the book.

Each time you go through it, you are looking (consciously or unconsiously) for specific information and other things, even if they stick out and grab your attention at the time, are likely to be purged by your long term memory because they didn't fit into the context that you were working within at the time. Or, what you are reading doesn't make a lot of sense or seem important or is confusing because you don't have a sufficient mastery of the material truly comprehend it.

How many times have you run across information where you discover something "new" but at the same time immediately remember having read it before? Chances are that was something the caught your attention but didn't get stored long term.

So every time you go through the book - and you can go through it almost randomly for a section here or a few pages there once you have read the whole thing once to establish the overall framework and basic understanding - you will learn a lot more.

And, of course, that goes for just about anything - from a textbook to a diet book to a set of regulations to your favorite fiction novel. Even movies.