Watch the Over Dominant Chords online guitar lesson by Rob Garland from The Guitarist's Pentathlon
The minor pentatonic scale is a great choice for dominant chords because of the tension of the minor third. A C7 chord contains the notes C-E-G-Bb, the Cm pentatonic scale is comprised of the notes C-Eb-F-G-Bb. Listen for the note Eb (b3rd) as it rubs up against the note E in the C7 chord (the 3rd). I played a musical motif that (hopefully) pulls the listener in, embellished it with a bend and the second time around added a fun "drunken Chuck Berry" lick. Remember to leave space between your phrases and try to build a theme.