Decide your purpose for reading. Has it been assigned to you or is it for extra or background reading? Think about what information you need to get from the book. This will help you to focus.
Scan the book's chapter titles, subheadings and pictures to identify which areas are going to be most useful to you.
Read important passages three times. The first time will give you an overview, the second time to fully comprehend it and the third time to consider it in your own words.
Make notes in the margins of your book or in a notebook. Highlight important passages with a highlighter pen. You can do this in conjunction with your third time reading a passage when you're putting it into your own words.
Review the information over the next few days to make sure you've taken it in and remembered it. Write a summary of the information or answers to questions you think will come up regarding the book.