The II V I in the key of C is normally expressed as Dmin, G7, Cmaj7. What you’ll find is, that the dominant chord’s ability to take disonance is much greater than any other chord. The first simple trick to get yourself some more outside notes is the tritone substitution. The way this works, is you take the G7, and play like it’s a dominant chord a tritone away, is this case, the tritone substitution would be Db7.
The reason this works so well is this: the third and seventh of a G7 chord are B and F. The third and seventh of a Db7 chord are F and Cb (or B). So the notes with the strongest “tendancies” are shared by these chords.
So if you were soloing over this Dmin G7 Cmaj7 progression, you would just treat it as, Dmin Db7 Cmaj7. It’s not necessary for the band to know because all the notes from a Db mixolydian scale work: Db Eb F G Ab Bb B. This gives you a fully altered version of G7 (we’ll be getting into altered later, suffice it to say, these notes work well against a G7 chord).
You can also apply major pentatonics to this concept. Try playing F major pent over Dmin, then Db major pent over G7, then D major pent over C. It gives a nice, strong, outside sound.
Incidentally, this trick works over static dominant 7 chords too. Take the song “Brown Eyed Blues.” The bass solo is over a B7 chord, so you could start in B, then move to an F mixolydian or major pent scale, then back to create some interest. It also works in blues changes. If you’re playing an F blues, trying treating the fourth bar as a B7, resolving to Bb7 in the fifth bar. Enjoy!