Jazz in your blues
Long ago I had picked up "All Blues for Jazz Guitar – comping styles, chords, and grooves" by Jim Ferguson. This book is about putting some jazz in your blues (or some blues in your jazz?). When I considered myself an "intermediate" guitar player and had the opportunity to play in jam sessions with musicians, who were well ahead of me, this book gave me plenty of good pointers. It allowed me to understand how music can become less rigid and without boundaries, how rhythm and melody can play off of each other, and how music theory can become practice.