Do you know any tips and tricks how to write a book review rapidly and painlessly? Or, maybe, you know any beneficial topics that always work?
I would suggest that if you have indeed read the book, write down a few things that stood out for you about the book. Choose a few keywords, focusing on how it made you feel, whether or not you found it an easy read or struggled to get into it, if it reminded you of anything else etc. I always find that first providing this framework for myself gets my creative juices flowing as I simply then need to flesh out around my initial idea or feeling. For example, if the book made you feel emotional, you could write that the story was relatable and brought a smile to your face or a tear to your eye. If it was easy to read you could describe how you found it hard to put down.