Read every word, including the acknowledgements section if there is one. Don't skip paragraphs or skim pages, because you may end up missing parts of the book that may be vital to your review.
Take notes while reading the book. If you are reviewing fiction, you might want to take notes about the characters, the plots and the settings. If you are reviewing non-fiction, you may want to take notes on things like themes and accuracy. Write down anything about the book you don't understand or that bothers you.
Figure out what the author is trying to say in the book and what his motives are. Does the author seem to have an agenda? Is the book slanted in a certain political direction?
Decide how long your review will be. If it is for a school assignment, odds are the teacher has given you a guideline on how short or long your review has to be. Book review length can vary greatly, so if you want to have it published somewhere contact that publication and ask what their guidelines are.
Go over your notes several times, making sure you have noted all the important things you want to cover in your review. Scratch out the things that you don't think will be important and underline or highlight the things you think need to stand out.
Outline what you want to say in the review in the order you want to say it. Make a list of the main points you want in your review.
Re-read your outline to make sure you have everything down the way you want to write it. Highlight or underline the parts in the outline that you want to pay extra attention to while writing the review.
Write the review. Make sure that you keep the entire review impartial and that you don't put your opinions into the review. State just the facts and back quotes up with specific page numbers.
Spell check it, read it least twice, and ask a trusted friend or family member to read the review to confirm it makes sense.