In this video I practice using a 4 note cell or “tetrad” consisting of just the 1st, the 9th, the 5th and 13th degree of the major scale. In C this would be C, D, G and A. An interesting thing about this specific tetrad is that, since it contains no 3rd or 7th it sounds great for improvising over Major 9, minor 9 or Dominant 9 chords. This means that just working on this one tetrad will potentially cover a lot of harmonic ground and practical application. Also, be placing the tetrad in a different location in the harmony, i.e. built off the #11 on a Dominant 7th chord, it can easily imply altered harmony i.e. G7 (C#, D#, G#, A#) or #11, #5, b9, b9. I practice the tetrad in various ways in all keys. Doing this over time will lead to a fluidity in its use.