Known as "The Principles" by the community of people who use this book as a teaching method, The Principles of Correct Practice for Guitar is a complete method for how to discover and maintain the best body positioning for playing guitar. While many would argue that there is no "best" method, there will generally be an ideal playing position and method for any given person depending on the shape of his/her body and guitar. This book helps you find that position and get back to it if you stray.
The main problem that must be addressed with guitar practice is the release of unnecessary tension. Tension that pulls your fingers away from what they should be doing is the main cause of most playing problems, and unfortunately it is a habit that ingrains itself with most players. This ingrained tension is what stops people from developing skill with the guitar, and the main purpose of The Principles is to give the reader an awareness and practice method to eliminate that tension.
As such, the exercises in this book might seem ridiculously simple to one who doesn't realize the problem of tension. Indeed, to remove our ingrained tension we often will have to go back to square one. Before you can attempt something as complicated as a scale, you must be able to fret over multiple strings perfectly, and before that can be done, you must fret a single string perfectly, and so on, all the way to the basic position you sit with the guitar.
If this sounds like a pain, it must also be known that the results in ability gained are extraordinary. Once a person has realized how to practice correctly, they'll wonder why they had been doing it any other way.