Instructions
Ask your student to take one ball or other small object in the right hand (or left if he is left-handed). Throw the ball in an arc, about eye level, from hand to hand.
Add a ball by taking one in each hand. The student should throw the ball from her right hand in an arc to her left hand. About halfway through the arc, toss the ball from the left hand over to the right hand.
Practice with 2 balls until your student can learn to do it smoothly. It takes a great deal of coordination and concentration to juggle two balls, so teach your student to do this move seamlessly before moving on to 3 balls.
Include one more ball, for a total of three. With two balls in his right hand (or left if left-handed), have your student begin by throwing one ball from the right hand to the left. Mid-way through the arc, throw the ball from the left hand to the right. Halfway through that arc, throw the other ball from the right to the left hand. Repeat, and your student is juggling.
Work on standing still. Many new jugglers feel the need to continually walk forward as they juggle. Teach your student to stand against a wall or bed in order to stay in place.
Avoid having the balls collide in mid-air by instructing the student to throw the third ball in a higher arc than the first and second.