STEP 1 : Throw your 1st ball straight up.
STEP 2 : When it reaches the top of your box, throw your 2nd ball on the inside of the 1st ball.
STEP 3 : When the 2nd ball reaches the top of your box and you have caught the 1st with your right hand, throw your 3rd ball on the outside of the 2nd
STEP 4 : Catch the 2nd with your left hand and when the 3rd reaches the top of the box, throw your 2nd back up the middle.
STEP 5 : Then throw your 1st and catch the 2nd with your right hand.
If you want to be flash you can stagger the throws so that they all go up at different times. When you juggle like this it feels like your juggling is limping.