After plugging away for a week, I was getting into something believable and needed another chord. I had A and E7, tonic and dominant, so clearly the next move had to be the sub-dominant, so I moved the E7 shape down two frets to D7.
There was nothing useful for the bass alternation on an open string, so I had to put it in by moving finger 3 on the left hand from the D on the fifth string to the A on the fourth string. As the right hand was becoming more automatic, this wasn't too hard.
For a little more variety, I started leaving out the first note in the treble, starting the treble line instead on the second beat. Try it either way—starting with the higher D on beat one as in the ossia (the name for extra bars over the score showing an alternative) or on beat two.
Once again, applying a little variety might be easy, so I took the first finger of the left hand off, and tried it with the first treble note on or off. At this point it might start to get confusing as you're moving two left hand fingers along with all the right hand action, so take it slowly. Remember to think along the bar in vertical slices: bass and treble.