For truly serious books, I recommend the following.  Read it once, straight through, with a minimum of fuss.  If you get truly, totally stuck on some point, which the rest of the book depends upon, find somebody to ask.  Otherwise just keep on plowing straight through.

Then write a review of the book.  Or jot down your notes, but in any case force yourself to take definite stances by putting words down on paper (or screen).

Then reread the book carefully, because now you know what you are looking for.  Revise what you wrote.

Of course only a few books a year (if that many) need to be read this way.

Marginal Revolution