Watch the Letter to Alfred online guitar lesson by David Hamburger from Essentials: Fingerstyle Blues
This tune goes by quickly, so I played through it twice here. For the first eight bars, all the melody notes you need pretty much lie right under your fingers as you fret the open A minor and F chords. At the turnaround, the melody gets more intricate, but when playing fingerstyle, we only need to fret the strings we’re actually going to pick. So for the Bmin7b5 chord; just hold down the root, use the open D string for the b3, and grab the melody notes on top. Likewise, on the E7, the open 6th string provides the root of the chord and the open D string serves at the b7, both good bass notes for the thumb.