To play down-strums and up-strums together put your hands in place: little
finger of your left hand on E1, thumb of your left hand on E2, thumb of
your right hand on E3 and little finger of your right hand on E4. First
play E1 with the little finger of your left hand. Next play E3 with the
thumb of your right hand. Now play E2 with the thumb of your left hand.
And finally play E4 with the little finger of your right hand. Repeat this
exercise a few times until you begin to get a feel for it. Remember, the
little finger of the left hand is followed by the thumb of the right hand,
then the thumb of the left hand is followed by the little finger of the
right hand.
Don't forget - alternate between both hands, and between thumb and pinky.
In this way, a down strum is followed by an up strum. Don't play the same
note twice in a row - or the instrument won't sound as real.
Our "rocking" style (alternating left hand/right hand, alternating
thumb/pinky) is easy once you get used to it, but it requires a little practice.
Remember that your left hand is the down stroke, the right hand is the up
stroke. For each chord, there are two samples for the left hand and two
for the right. This adds much more variety and realism to the sound.