An interesting topic that I found from other composers is the use of the blues arpeggio. It looks something like this:
Just like how you can arpeggiate the chord harmony, the blues arpeggio works great over dominant-seventh chords in the blues format.
Notice that even as you are going down in the arpeggio, the lowered-third comes before the raised-third. This is so you can obtain that classic blues slide sound as well as the microtonal blue note in-between. Of course, this is a preference, not a strict rule.
In addition, just as the chords change in the 12-bar blues format, so will the arpeggiation. It does not stay strictly to the key signature; more so, it is determined by the root of the dominant-seventh chord.
Try practicing with them!
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