While this book alone will introduce you to concepts and refresh your memory on topics you may be less familiar with, you can maximize your studies by practicing and exploring what you're learning first-hand in an actual tenant.
As you'll find in this book, it's recommended that you get a Microsoft 365 E5 subscription in order to explore, but you could also combine a Microsoft 365 E3 trial with an Enterprise Mobility and Security E5 trial to cover most of the book's topics. In the end, what matters most is that you make sure you get a trial or a subscription to the services and apps you feel least confident with so that you can spend time exploring them first hand.