Combinations I use include:
Bass/Melody #1 - Right hand for bass lines E and A string, and the left hand for melody lines D and G string
Bass/Meldoy #2 - Right hand for bass lines A and D string, and left hand for melody lines G string only
Appegio's - Right hand E and G string, left hand A and D string
I also like see the whole fretboard for choices of notes use:
