Know the author: Know his/her bio. Understand his bias and perspectives
Summary of the book: Google for the summary of the book. Read the reviews about the book to get the picture.
Read the Title, Subtitle, Front flap and the table of contents: Try to Understand the Big picture and the arguments laid out in the book.
Read the introduction & conclusion
Skim each chapter: Just understand how each chapter is dealt with. Read the first and the last line of each paragraph. If you can understand go ahead. If not, go into it.
End with the table of Contents: Once again go back to the table of contents and relive the follow of the books.