I struggle with this as well. I am not working on improvisation per se but I’m trying to get better at writing riffs and solos.
One “simple” concept I’m finding useful is this: memorable solos tend to be a good compromise between repetition and variation.
Too much repetition and it sounds boring, too much variation and it will sound like a collection of random licks.
A vaguely related concept is “call and response”, which is easier to illustrate with an example.
So you could have something like:
idea 1 (first call) , idea 2 (first response) , variation of idea 1 (second call) , idea 3 (second response)
Of course not all great solos follow these ideas, but this is one possible way to go about it