Writing a book review for an academic journal is a great way to start getting publications on your CV. You should follow certain general guidelines, especially if you are writing a review for the first time, as a graduate student, or even as an undergrad.
How to Write an Academic Book Review
Do not write a book review on spec. Most academic journals solicit their book reviews from people acquainted with the editors or from those who write requesting to write a review. Your first order of business, then, is to draft a letter of inquiry, stating your background and that you would be interested in writing a review for a journal. If there is a new book you know you would like to discuss, feel free to ask. For the most part, however, editors will send you a book which they need to be reviewed.
Read the book. While reading, it is important not only to take notes about the book's content, arguments, data sets, etc. You also need to know how the book wants to intervene in the current scholarship. With what other trends and/or authors does it argue? What methodologies does it use (or change)? How original is the work? How successfully does it make its arguments?
When writing the review, pay attention to the journal's guidelines for review formatting. If the editors did not provide you with a format sheet, read a number of recent reviews in that journal to see how they work. Check for length, general use of quotations, relative balance of summary vs. critique, etc.
Do not summarize too broadly. As an academic reviewer, remember that you are writing for a very knowledgeable audience, particularly about the topic under discussion. You will not need to introduce every concept in the discipline as you can assume that anyone interested in your review will already be familiar with the field.
Remember that most academic books are works of professional conversation and interaction. Even if a book is personally irritating to you, your job as a reviewer is to introduce and evaluate the book for other professional scholars. Be charitable in your summary, taking the book on its own terms. When you introduce your own criticisms and reservations, articulate them in a way that other professionals will find helpful. Make suggestions about how the argument might have been improved, how the selection of primary and secondary sources could have been more effective, or what other works might address the same topics in better ways.
Discuss clearly how the work might alter current scholarship, pointing in new directions or opening new fields of questioning. If you feel that the book is misguided, suggest how further scholarship might assist in overcoming the drawbacks in this work.
Conclude with some advice on whether and how other scholars should use this book in their own research.
Avoid jargon. Even if the author uses disciplinary jargon, your review should present their argument in its clearest terms. Do not attack an author personally. Especially if you are a young scholar speaking about a more established author, you do not want to make enemies since someone somewhere will have to review your work as well.