I found this book to be pretty easy to understand with very accessible language. As someone who works with authors to help them make their books better, I need to have a solid understanding of different types of POV, how to identify violations, and offer suggestions for fixing problems. This book is organized in a way that makes it a valuable resource for referencing later on.
If you’re an author, there are loads of exercises that can help develop skills, too.
I highly recommend all authors pick this up.