You can start with any, but I recommend
"Guitar Zen: CAGED" the blueprint for how I see everything!
"Guitar Zen: Next Level Rhythm" is a continuation of CAGED. It goes into intervals and grooves, and how to create your own tasteful guitar parts.
"Guitar Zen: Playing The Changes" is the chillest way I know to surf across chord progressions.
"Guitar Zen: Pentatonic Doublestops" goes into the "Hendrix-y" side of rhythm playing.
"Guitar Zen: Improv Strategies" Simple ideas can yield the most soulful results! Rhythm & Repetition, Call & Response, Moving Motifs, and all of my favorite "tricks."
"Six String Problem Solver" was created in response to seeing what students most often struggle with. I devised little exercises to address the various little annoyances us guitar players face.
"Modes" uncovers the harmonic and groovy side of all 7 modes, as well as the melodic. The progressions and jams that are often overlooked - we can finally understand them!
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