Identify the author's key words, the few very important words that the author uses again and again. Look the key words up in a dictionary and figure out how the author is using them in particular.
Question the text. Do not accept everything the author says as the truth. Struggle with the ideas presented in the book. Think critically, asking yourself questions about the contents of the book and about the author's motives.
Locate the author's arguments. Determine what judgment the author had made and how he has crafted his argument and is trying to convince you of its validity.
Judge the author's argument for soundness and completeness. Follow the logic of the argument to judge its soundness. Ask whether the author has adequately solved the problems he set out to solve or answered the questions he set out to answer to judge completeness.
Read information outside the book you are reading. Study multiple authors writing about the same subject, each developing his own independent argument. Analyze each author and the discussion as a whole, starting from the more general parts of the discussion and gradually looking at more specific aspects of it.