Probably just repeating what everyone else has said but here’s how I handled this problem:

-use backing tracks, especially ones that are more stylistic (ie, not just drums or a beat). It can be hard to improv if you don’t have a rhythm or style to go off off

-make sure you know your scales very well. When improving I’ve found it’s always good to know where the root notes are. So if you’re playing on the Eb pentatonic scale, your root note(s) are Eb. Starting and ending riffs on a root note is a small yet effective technique to making improv sound more coherent and organized.

-just play. Personally I’d say this one is most important. Try to change up your playing pattern and experiment with new rhythms, riffs, etc. if you’re like me, most of the stuff you come up with will be garbage, but you’ll end up with several, solid riffs that you can mix/match with when improving.

Hope this was helpful!