Thumping out a steady bass drone with your thumb lets you spin bluesy, single-note licks over the top with your fingers as an improvised alternative to the folkier-sounding alternating-bass style. The following examples should help you get coordinated in this steady-bass style. With a little work, you’ll be able to keep yourself entertained for hours on end.
Ex. 1 is about getting used to the roles your thumb and fingers are going to play. Ex. 1a gives you the steady bass in quarter notes on the low E string. In 1b, you pinch the high and low strings simultaneously on the downbeat, then continue to carry the bass for the next three beats. In 1c, pinch the high string on the first and third beats, always maintaining the bass with your thumb. In 1d, make the pinches on the first and second beats only, and in 1e on the first and fourth beats.
Ex. 2 introduces the idea of eighth-note syncopation. Make the first pinch on the downbeat, and then repeat the note–that second note on the high string falls between the first and second beats. Examples 2b through 2e introduce fretted notes on the B string and involve similar eighth-note syncopations throughout each bar. You can practice each of these examples as a continuous loop: keep the steady bass going and just keep playing the one-bar lick on top over and over until it feels comfortable (or until your roommate/spouse/significant other threatens to do mean things to your guitar with a wire cutter if you don’t knock it off).
Excerpted from Best Private Lessons