Read the novel one time without doing anything else. Then read it again and take notes as you write about things that catch your attention (positively or negatively) questions you may have and anything else that makes you think twice. Place Post-it notes in the pages where you want to remember a quote or specific passage.
Write a short summary of the book as you read it. Sometimes the provided synopsis has a different point of view and the review needs to come from your perspective.
Do some online research on the author. Sometimes understanding where the author comes from and what she usually writes will give you a unique perspective of the tale or change your notions about the story as a whole.
Make a list of all the points you want to express and address. Write your review based on this information.
Set the review aside for a day after finishing, then return to it and read it again. A fresh look at it may reveal typos or inconsistencies in your wording, or give you a better idea to improve it. You can also have someone else read it and give you an outsider's look at your work. Have fun!