Here is a lesson I gave a student today. The student is not a beginner, but a happy amateur who learned to play jazz in his 70s and now in his 80s plays each week in a jazz band.
Beginning improvisors need to prepare the harmonic and melodic elements before they commence. I suggest the following exercise to him.
1. Listen to multiple recordings of the piece.
2. Mark in the ii-V-I progressions and identify the keys they are associated with.
3. Practice the major and natural minor scales associated with those keys.
4. Practice the broken chords in the right hand.
5. Practice voice leading the chords in the right hand as shown at measure 70.
6. Practice linking them together in 8th note melodies as shown at measure 75.
7. Practice with chromatic approach notes before the 1st chord tone as shown at measure 79.
You've got to learn your instrument. Then, you practice, practice, practice. And then, when you finally get up there on the bandstand, forget all that and just wail.
I'm a professional pianist and music educator in West Toronto Ontario. I'm also a devoted percussionist and drum teacher.