Gareth asked me to review his latest book 3 Shape Fretboard, which I gladly did because I'm always interested in new educational guitar books, not least because I spend quite a bit of my time teaching students. The book is about learning to play and understand scales on the guitar. The emphasis is on understanding as opposed to just memorizing dots on the fretboard. You learn to think in intervals and to immediately see these intervals on the guitar. You'll go through all important scales, like the major scale and its modes, harmonic and melodic minor scales, and pentatonic scales. All scale shapes are reduced to three basic shapes that you will manage to find very quickly everywhere on the fretboard, no matter what scale or key you're in. It takes some effort but working through that book will give an immense boost to your scale and fretboard knowledge.
If you want to know more about the book and what I think of it, please read my complete review on Gareth's site (scroll down to "3 Shape Fretboard" and click on my name).