The best attack on this problem is to download some templates from the websites of well-known journals, read them carefully, and follow the steps to make a template for yourself to use whenever you want.
If you are reviewing a book, you should describe the content of each chapter and bring to the fore the novelty (if any) in each one.
You can describe the strengths and weaknesses of the work as a whole, by having in mind the contributions that the work has made to current scientific knowledge.
Of course you have to make references to current literature in support of your statements (so you shouldn't only describe the content of the work you are reviewing).
Remember to adhere to the house stylesheet and to write within the given word limit.
You will need to follow some steps, here are some that I usually take:
1. Define Your Scope (the words and concepts on it will be your key-words for the databases search)
2. Conduct the Literature Search (Use multiple databases (e.g., PubMed, Scopus, Web of Science) to ensure your “coverage”.
3. Organize Your Findings (Group the literature into categories)
4. Critically Analyze the Literature (you could compare methodologies, results, etc.)
5. Structure Your Article (it depends on your field, but may contain: Introduction: State the topic, scope, and significance. Define key terms. Methodology (if applicable): Describe how you selected and analyzed the literature. Analysis/discussion.
6. Seek Feedback (for a preview before you send your manuscript to a journal).
7 Submission (find a journal or consult your doctorate supervisor to hear his suggestions; follow the instructions of the journal; wait for the peer-review.