Watch the Into The Cage online guitar lesson by Brad Carlton from Chord Studies: CAGED Chords Vol. 2
This progression is a V - IV - I in the key of A. We're employing the CAGED system and are using the forms that the system is based on because we're down in open position. When switching from the E to D, utilize your first finger as a guide finger, sliding it up one fret. When switching to the A, your third finger will be a guide, and your first finger will be a pivot, meaning that it doesn't move.