Watch the The Thumb online guitar lesson by Muriel Anderson from 1-2-3 Fingerstyle Guitar
Chet Atkins used to say that he spent a couple of years just moving the thumb back and forth before adding the melody.
Playing accompaniment and really listening to the groove and getting your body to move with the music is a good first step to playing fingerstyle guitar.
We'll work a lot with the movement of the thumb, and moving the arm and body as well. There are also different ways to detach or muffle the bass notes for a crisp and distinctive sound.