First, tell your audience what the book is about. Give your readers a taste of the book, preferably without going into any plot twists you would not want to know before reading the book yourself. Tell about significant ideas in the book, and include carefully selected key events. You may choose to name important characters and discuss their significance as well.
Second, let your readers know whether or not you think they should take the time to read the book. After all, a book requires an investment of time, a finite resource. Of course, you will support this recommendation with specific reasons. Throughout your essay, allowing the author(s) to speak through direct quotations will make your review stronger and help you support your claims.
As you write, keep your responses on the Form for Book Review handy. You have the choice of writing a positive review that recommends the book or a negative review that does not. Alternately, you may write a mixed review that acknowledges both positive and negative attributes. Ultimately, however, you should come down on one side or the other. Keep in mind, also, that the more mixed a review is, the harder you will likely find writing it. Take care to use transitions like first,next, second, third, later, meanwhile, before, earlier, after and finally to move from one idea to the next.