Hi Johnhenry, take a simple melody such as "freight train". (Key C). Pick the tune using your middle finger only and confine your playing to the first three frets. When you have "mastered" the tune then use you thumb alone to pick out the base accompaiment confining your playing to the e and a base strings (hum or whistle the tune while you do this). Then you revert to playing the tune (middle finger only) and introduce the base accompaniment(thumb only). Hard for a beginner but persist and it will become second nature.