I've heard a lot about Mr. Werner's Effortless Mastery title. In fact, I know a band whose two primary musicians constantly bicker about whether this "effortless" approach is viable. After years of hearing about it, I decided to find out for myself.
The book starts out with one basic premise: you are an aspiring, practicing musician, looking to "break through" to higher grounds of playing. Many people are at this stage, but have a fear of unfamiliar musical territory. The bulk of this book is dedicated to removing this fear.
Werner's approach to doing so is by breaking down negative programming that's been beaten into aspiring musicians worldwide throughout their music careers. Some have a fear that's instilled by their teachers, who constantly tell them they're not good enough, not perfect enough, not smooth enough. Others have this fear imbued by "great" musicians - those who seem to push the boundaries and perform inhuman feats on their instrument. According to Mr. Werner, all this negative programming eventually becomes an insurmountable barrier for advancement - unless it is reversed and positive programming is imposed on the musician. Who will impose this programming? Most likely, it will be the musician himself.
Again, the basic premise comes into play: you must work on your technique, learn new music, and address your weaknesses. That is a given, and there is no way around it. However, you must also have a positive outlook while doing so - otherwise all the imperfections you've ironed out during practice will come back to haunt you in performance.
Some of the initial chapters reveal in great depth Mr. Werner's personal experience. In his younger years, he went through all the negative programming himself, and has learned (and continues learning) how to reverse it. It is from the standpoint of this experience that he approaches the subject-matter.
Through gradual guidance in the later chapters (and the three meditations on the included CD), Mr. Werner tries to help the student create a personal space, in which the student is master. By revisiting this space and learning to practice and perform from within this space, the student will become the master and reveal his inner voice. Don't expect to become an overnight master effortlessly, however: Werner suggests that learning to play from within the space will require relearning the instrument from scratch. This is a slow process at the beginning, but becomes natural as time goes by.
Unfortunately for many, a lot of the points made in this book are self-evident, or at least should be. Nonetheless, his encouraging tone instills the belief that mastery is possible. In the end, the student will hopefully realize that mastery is, by definition, effortless.
Some sections of this book are specific to particular instruments. Werner is a pianist, so quite a few examples are piano-related; he also talks about some other common jazz instruments, notably wind and brass. To my dismay, the guitar isn't mentioned, but the general pointers in the book allow this approach to be taylored to any instrument, and even to activities beyond music and arts in general.