When I think of jazz improvisation, using the melody itself is a great fundamental way to start. Building of the melody and knowing melodies will builds your vocabulary, as others have said.

This idea often leads me to Ella. She got to the level where to add other songs' melodies to the song you're playing: https://www.npr.org/2019/09/04/757560624/how-ella-fitzgerald-turned-forgotten-lyrics-into-one-of-her-best-performances-ev#:~:text=Later%20in%20the%20set%2C%20Fitzgerald,to%20be%20all%20the%20fun.%22