Sometimes we're called upon to improvise over just one chord for long periods of time. To keep things from getting too predictable,  I like to employ a "chord on chord" approach in situations of this sort, implying moving harmonies over the static background harmony. In the following example, I played over a C7 vamp for 12 bars. The "inside" (consonant-sounding) parts of the solo imply basic chords like C7 and Gm. The "outside" (dissonant) lines imply C13b9, F#13 (or C#m) and F#m. I've listed scale choices for those who prefer to "think scales", although I personally tend to come up with this stuff by thinking about chords.

Why F#13? Because it contains the #11, 7, b9, #9, 3, and #5 of C7. Alteration city - plus guide tones!

Same thing with F#m: it has the #11, 13 and b9 of C7. If I extend it to F#m9, it also has the 3 and #5.

Notice the progressive dissonance in the solo; it starts out pretty close to the basic C7 chord, then the alterations come creeping in. The passage wraps up with a good ol' blues lick to bring us back home. This "in-out-in" idea can be used as one way to help give shape to a line or solo.

Play Example