Figure A gets us started with a C Minor Blues progression.
C Minor pentatonic (C-Eb-F-G-Bb) will be a common choice for many when improvising over this. Another option is C (natural) Minor, which is played C-D-Eb-F-G-Ab-Bb. Give them both a whirl and see what you come up with. Let your ears tell you if there are notes that work better than others (which, of course, is totally subjective).
Digging into the theory behind this progression gives us some more information. Cm is played C-Eb-G, Fm uses F-Ab-C and G7 equals G-B-D-F. If we sort through those notes, do they all fit into the C Minor Pentatonic of C Natural Minor? You’ll notice that the B note in the G7 isn’t in either of those scales.
It might be worth playing a B natural and B flat note at the same time and have a listen. It can be rather clashy (especially in the context of the C Minor Blues and G7); however, you could also play over the progression and possibly not hit a Bb over the G7 too.
If you want to add some spice to your playing and want to hit some more chord tones, try playing C Harmonic Minor (C-D-Eb-F-G-Ab-B) over the G7 chord. C Harmonic Minor contains all the notes of G7 (G-B-D-F) so you can outline the chord, but also has the b9 (Ab) and the #5 (D#/Eb). These notes add some great additional colour to your sound.
Try playing C Harmonic Minor over the G7 as a starting point (just as crotchets or quavers, ascending and descending) to get the sound into your head. Once you’re feeling comfortable, you can then start making phrases and playing the intervals, note choices and rhythms.
Figure B has three example licks to play over the G7 in the last bar of the C Minor Blues. These outline some (or all) of the G7 chord and emphasise the B natural from C Harmonic Minor as well as the aforementioned Ab and D#/Eb. Try playing C Minor Pentatonic and C Natural Minor over the Cm and Fm chords, but use C Harmonic Minor over G7. You’ll hopefully start creating some cool sounds and licks pretty quickly.
Image via Jefferson Santos.