I enjoy crafting harmony tracks with which to practice. They are not usually jazz, but instead are more ethereal.
Here's one I like because the harmony slowly becomes more complex and ear-stretching.
Things to do with them:
- Sing some scales and melodies over it in order to get your ear in tune
- With your instrument run F major scale up and down its full range. Vary the dynamics and articulation in musical ways.
- Do the same with C major scale (F lydian).
- Do the same with Bb major scale (F mixolydian).
- Play a melody you know really well in F or C or D or any key.
- Find and play the colorful notes in the harmony.
Most of all, have fun with it!