Lately I have been having fun layering parts over top of progressions of songs that exist already. A solo of sorts.
The following was written over a middle section in the key of D with the progression D A Bm G.
Here is the theory behind this. The progression four beats for each chord in the progression at about 70BPM. So the thought process is targeting chord tones at the right time, while supplying some flavor in between. It’s all D major pentatonic.
I start on the root (D) of the first chord, hit the third (F#) of that chord, and target the root (A) of the next chord. I play around a bit with A and B (the next chord in the progression), but instead of the root, I hit the 3rd (D) which also brings us back to our original tonality of D
I slide up to the fifth of the Bm (F#), pull of F# to E and land on D again. This time D is the fifth of the next chord (G).
Then I just walk that back down, playing in pentatonic and land on the D again. But an octave up this time. I run that same pattern again of D - F# - A, but this time I use a dyad (2 notes of the chord) for some flavor. I repeat the A - B thing again, but with a little more space. And go up and hit the third, for basically the crescendo of the part, and just gradually walk back down to D chord.