When I studied jazz a long time ago with Bob Winter at Berklee, he told me there were two important things to remember about improvisation. One- the musician is the chief orchestrator, and two- learn a lot of material. Initially, I thought he meant jazz standards. But the musician who improvises must constantly explore many styles of music.
What does this mean? I am an avant-garde new music improviser, but I am constantly discovering new composers from different genres- in listening and reading.
My practice different genres which affect my improvisation. Jazz, Bach, Shostakovich, Prokofiev and an array of composers who affect my music consciousness.
The same goes for listening- I listen to many genres from rock, new jazz, older jazz, swing, Shostakovich, Prokofiev, Bach, Beethoven, Mozart- a large list of great musical contributions.
A musician’s improvisation will continuously develop by listening and playing many different genres.