According to the blurb on Amazon, "Mastering the Law School Exam is designed to provide students with a knowledgeable, reasonable, and rational voice to navigate the intricacies of law school exams. This book is practical rather than theoretical where the emphasis is on providing the type of detailed examples necessary to show students precisely how to do it and how to write it."

Generally, I think this book is better suited for those who have already taken a round of exams and want to improve.  That's partly because of its length and detail. As you begin law school, you may not have the time to devote to reading another book.  But if you can, do.  Just remember, it's the kind of book that you really need to commit to if you're going to expect it to help.  In other words, don't try to breeze through this.  

So, if you are able to spend time each week going through the book and using it on a progressive basis ... start as early as you can afford the time.  In the first few pages of the book, Professor Darrow-Kleinhaus explains how to use the book to your greatest benefit depending on whether you are a beginning law student or a veteran.