Watch the A Chord Pattern online guitar lesson by Stephen Mougin from Bluegrass Rhythm Evolution
An A chord is similar to the D chord. A string, strum, E string, strum.
Since your right hand has the D pattern already, you just have to move to the next lower string(s). If you are looking for a way to alter the sound of this one, try grabbing the extended A chord with your pinky on the high E string (5th fret A note).