Here's an idea. Take a tune, learn to play it. Next, play the first phrase as is. Then, take the second phrase and make something up. Then take the third phrase back on the melody again. Fourth phrase, make something up. You can hang on the tune to tell you where you are.

The best improvisors know the changes. If you know the chords of a song by memory, then you can relate to them in two ways. 1. Scalar or horizontal. 2. Chord arpgeggios or vertical.

To be able to hear the harmonies of a song, take the chords and change them to roman numerals. Then transpose them to as many keys as you can stand. Eventually, you will be able to hear the chord relationships independent of any specific key and express them numerically.

Once you hear the harmonic line independent of the melody of a tune, you are better able to fit your improvisation to it and you will always know where you are in the song without depending on the melody.

Frank