Watch the Changing Forms online guitar lesson by Brad Carlton from Chord Studies: CAGED Chords Vol. 2
This is a V - IV - I progression in the key of A. You'll start off by using the G form out of the CAGED system for your E chord. It's imperative that you keep your third finger upright so that you don't mute the fifth string. We then go to a D chord with the E form. When going to the A chord, barre across to the fifth string to help keep your fingers upright.