Ermmm.. I'll try.
Take the chord sequence Cm7, F7, Bb7.
You could decide to play Dorian on C over the Cm7 as Dorian is a minor scale and fits.
C, D, Eb, F, G, A, Bb
Then you might decide that you will play an F blues scale
F, Ab, Bb, B, C, Eb,
Then you'll take a Bb major scale for the third chord.
Bb C D Eb F G A Bb
Instead of thinking in terms of scales for each chord you could choose this method:
Cm7 is chord II of Bb Major
F7 is chord V of Bb Major
Bb7 is obviously Chord I of Bb Major.
So you use the Bb major scale for the whole lot.
You then choose your notes from that scale and miss out certain notes depending upon the chord underneath.
To make it more interesting you'll embellish with tones from outside the scale, like introducing the Ab over the F7 and Bb7 chord as the minor 3rd, then the 7th.
As the chords relate together a lot, the example isn't drastic. But when you have chords that aren't do obviously related or are substitutions, it gets complicated as you're note choices get very limited and it's often better to start looking at a new key centre.
If the next chords where C7, F7, G7. They'd all fit within a Bb key pretty easily, but it would be easier to think in C major over the three chords. with a I, IV, V progression instead of a IImaj, V, VIMaj progression in Bb.