Hi JC
Look at previous book reviews in same journal and see if you can pick out structure, and note word length - then frame your book review around that. Otherwise... basics:
What is the book and who is author - why have they written the book?
Who is the intended audience(s)?
Why would they want to read this book?
How well (or not) do they meet the needs/interests of the intended audience(s)?
What are the key points of interest in the book?
Are there any key concepts, links to other theories that are of interest?
Is the book coherent, relevant, up-to-the-minute (on the field of interest)?
What grabs you especially about the book?
Are there any areas where the book doesn't meet its aims well, where it could be improved?
Are there any bits readers might feel disappointed with?
Find a few examples, key quotes that support your answers to these questions and illustrate why you've said what you did.
Conclude with a summary - is book good, worth buying, why?
Hope this helps. :-)