Watch the Slow Blues online guitar lesson by Jeff McErlain from Blues Guitar Survival Guide - Lead
I love using thirds and sixths in my playing I think they add a very cool harmonic dimension you simply can't get from single notes. This study is reminiscent of Miles Davis's "All blues" from the classic Kind of Blue recording. It is a classic but it was Larry Carlton's version from the "Last Night" recording that introduced me to how simply harmonizing a melody in sixths can spice up a tune. We would usually see our top note (the highest note) as the melody and the sixth below as the harmony. Try it with some other melodies you may know, I have to stop myself from doing this too often!