Reviews are one of the best ways readers can help authors. Word-of-mouth is still the most effective advertising method. If you enjoyed the book, recommend it.
Reviews can be intimidating - even for writers. They don't have to be, though. Even a simple "I loved this book" is helpful. In fact, some of the shortest reviews are the best. Below are some hints that might help. It isn't necessary to tell what the book was about. That's what the book description, back blurb and editor's review is for.
Things you should not do in a review.
1. Never give a negative review on a book you have not read completely. Some books redeem themselves if you stick with them.
2. Don't berate the author. If you feel the need to criticize, make your criticism constructive. Most writers welcome feed-back that helps them improve their writing, but even prospective customers feel uncomfortable reading a review that berates the author.
3. Don't give false praise. It deceives other readers and does the writer no good. If you don't like the book, don't review it. Every book can't be the author's best and what one person dislikes about a book, another might enjoy.
Questions that might help. (It isn't necessary to answer every question.)
1. Did you like the book?
2. What was your favorite part of the book?
3. Did you relate to a specific character?
4. Would you recommend the book?
5. Did you have any strong emotions while reading the book?
6. Has this author written other books that you like?
7. Does this writer compare favorably to another author you like?
8. Do you normally read this genre?