Watch the Comp The Scale online guitar lesson by Chris Buono from 40 Day Rhythm SWAT Camp

Even when a progression doesn't have many changes, you can still be harmonically active. The secret is to "comp the scale." Here's how:
Determine the scale or mode of the moment. Select an interval structure for example, a pair of stacked fourths.
Keeping this structure, diatonically ascend and descend the fretboard, playing voicings drawn exclusively from this scale or mode. This technique works best when you're playing a one-chord sound for an extended period of time.

To get the hang of this concept, try comping a 16-bar Gblues progression using diatonic fourths. For the G7, C7and D7chords, we're in G, Cand D Mixolydian, respectively. Ex. 1 shows the seven chords for each mode.

Move through GMixolydian's chords playing only the lowest voice. Next play the middle and finally the top voice. Notice how no matter which voice you're tracking, you remain in GMixolydian. Now play the modal triads, freely moving up and down the fretboard.

Repeat this process for Cand DMixolydian. You're ready to use this technique musically. As you play Ex. 2, hear how the mode shifts every four bars. Record these changes and solo over them using the appropriate modes

Don't stop there: Comp the Dorian, Phrygian, Lydian and Aeolian modes!