Watch the Meet Your New Best Friends of the Jam: Guide Tones online guitar lesson by TrueFire from Play Blues Guitar 8: Advanced Rhythm Principles
Meet Your New Best Friends of the Jam: Guide Tones - Introduction is a video guitar lesson presented by Jeff Scheetz and is sourced from Blues Jam Survival Guide.
Guide tones are basically the 3rd and the 7th of the scale. That is because those are the most important notes of a chord, and will tell you what family the chord is from - Major, minor, or Dominant. So by just playing those two notes, you get a lot of information about the chord!