Improv over descending dominants! Trickier than it seems!
Chromatic descending dominant chords are actually a little more tricky to improvise on than they seem at first. You as the improviser have the choice of the approach - sometimes staying within the tonal center can work well, as the dominant chords move underneath your line they change the harmonic context of your line, which can work out in your favor!
Playing a line that moves through the dominant chords is a bit more tricky - there are some drills that can help to improve this, I am attaching a few youtube links for reference of some of my favorite chord tone drills. One of the simpler ways to get through these sections is to play off of chord tones, often the chords do not last that long so it gives a nice bebop effect. The more advanced, long term goal however should be able to imagine a line that fits into the tonality of each chord as they pass by… and then play that. Imagining solo lines through descending dominant chords is particularly hard as each chord changes keys, but by drilling the chord tones and exercises above you can prepare your imagination to do just that.
Thirdly, you can compose little improv sections that get you through the descending motions. Then practice them and learn them like licks. Do this five to ten times and it will start to give you some vocabulary to play in those sections, although it may not be the ’true’ improvisation we are searching for it still counts as improv to choose a lick to play in a certain place and in essence ‘arrange the puzzle pieces’.
I hope thats helpful!