Gail Carson Levine is known for her writing and here she shares her methods with her readers. Her guidance comes not only from her own writing but also from her work with writing groups of all ages. While this is aimed at younger writers the exercises are of value to all ages.
I would say that the book is designed to be very interactive. I did not do the exercises as I went through but I would definitely recommend them even if you alter them. I have already used some of the exercises in trying to get past my current writing struggles. The book is broken down logically into sections, so it is also easy to reference the portion regarding what you are currently seeking help with.
This is a short book so this will be a short review. No book you read will ever magically transform your writing. You can only continue writing and what this book does is gives you things to stretch those muscles. It makes you think about what you are writing and encourages you to go beyond what you might have originally thought. The good thing about prompts is that they push you beyond characters and situations that you would normally write.