Compose an introduction containing the title, author's name and author's credentials. By listing the author's credentials, you can attest to the author being an authority on the subject. That validation allows your readers to better determine whether the author is knowledgeable enough regarding the topic.
Briefly summarize the book's content. Keep your summary concise, touching only on the main points. Try to limit this summary to one paragraph; an overly long and unnecessarily detailed summary may turn review readers off.
Discuss whether the text was engaging. While the ultimate goal of a science book is to share information, it is also advantageous if the text is engaging. Texts that capture attention are much less arduous to read.
Analyze the soundness of the scientific facts present in the text. Make reference to specific findings presented in the book, and explain whether they are verifiable or if, instead, they appear to have no scientific backing. Avoid nitpicking; keep the focus on the scientific value of the information.
Reference other important books -- and even articles or other bodies of work -- on a similar topic, comparing scope and content. By making reference to similar books, you can allow readers to see where the text fits within the genre and how it stands up against them.
State whether you would recommend the text and, if so, for whom. Give readers your final recommendation in a sentence or two. Clearly state whether the book is worthy of reading.