To get into open-C tuning, tune the low E string down two whole steps to C. Bring the A string down a whole step to G and the D string down a whole step to C. Leave the G string where it is, raise the B string half a step to C, and leave the high E string alone. From low to high, the tuning is: C G C G C E.
As you may know if you’ve done any single-note blues soloing with another guitar player or band, one of the great beauties of the minor pentatonic scale is the way the same phrases seem to work over all three chords of a blues progression. Try playing Example 1 for one fingering for an octave and a half of the C-minor pentatonic scale in open position.
Now let’s try playing a simple phrase worked out over an alternating-thumb accompaniment with a C chord, an F chord, and a G chord, as illustrated in Example 2.