In reviewing myself, as well as reading many other reviews (mostly online), I have many dull opinions on how book reviews should be undertaken, including the following points, which are too often neglected:
Before reviewing a book, it’s important to read every other review you can find, to reference these reviews in yours, and to build upon what you have learnt from them. Reviewing should be a conversation, not a series of monologues. The reader isn’t interested in what you could come up with on your own; the reader is interested in the book. Your opinion alone is not sufficient. Any insight you have into the book is going to be improved by reading what others have thought of it, even if you think them wrong. There is never any reason for not reading other reviews before you write your own.
Furthermore, it is useful to at least make a brief attempt at familiarising yourself with the writer and the publisher. It mostly isn’t feasible to read something else by the same writer, even if this would be ideal.
Already mentioned, but worth emphasising. When you are reading other reviews, you should be referencing them (which, in the world of online poetry reviews, means linking). If someone expresses an idea better than you could, quote them.
3. Show your working
Give evidence. Don’t expect readers to take your word for it. This is especially important if you feel a book is bad. If you are going to give a bad review, have the respect for your readers, and for the writer whose book you are criticising, to show why the book is bad, to lay out the specific areas which you think are poorly done. The worst review is the one which declares ‘Do not buy this book’ and says little else. Again, your opinion alone is not sufficient. Conversely, if you think a book is great, show what’s so good about it.
4. Don’t fear the reader
You should always assume that your reader is smarter than you are. Whilst reviews might quite not be the place for exclusively post-structuralist terminology, for instance, if you have a good idea which only works in relation to post-structuralism, don’t feel you can’t discuss it. Don’t simplify your ideas for fear that the reader will be confused or put off. On the other hand, if you can’t express something intelligibly, you shouldn’t be trying to express it at all. If you’re clear enough with your examples the reader should be able to see any point you’re making for themselves (see point 3).
A review is better if you find one point to focus on, and show the strengths or weaknesses of a book through a central idea, rather than trying to cover everything. (Point 1 applies here, as having other antecedent reviews will help to do some groundwork and suggest the point one which you may wish to focus.) The review will be more interesting to read, and it gives a chance to move straight to some concrete examples (point 3 again).