Memphis blues originator Furry Lewis called Vastopol the learning key. With the tonic note on the lowest and highest strings, it’s easy to play bass and melody at the same time. Basic chord shapes in the first position are also easily formed. The open D chord affords an octave bass line on the sixth and fourth strings with the option of adding the A on the fifth string. The low D, although technically part of the G chord, is best left out; a fifth-to-fourth-string bass part gives an effective third (B) in the bass. Likewise, the A7 is also a five-string chord. (This voicing has no third in it.) Thumb through these changes, then practice playing these simple arrangements of a couple of folk songs.