Set-up: Mark 4 spots on the ground in a square. You can use tape or chalk, or even a removable marker (verify it can be removed!) for this purpose. Mark the top left corner a 1, the top right spot 2, the bottom left spot 3 and the bottom right spot 4. When you first start, mark the spots about a foot apart from each other, and progress the distance gradually as you feel comfortable.
Movement: Jump from number to number, landing on your toes and quickly moving to the next point. Speed and quickness - not length or height of jump - is the goal. Once you have reached the fourth spot, jump backwards through the loop. The full cycle will go 1, 2, 3, 4, 3, 2, 1. Count each individual jump as one repetition.
Emphasis: Keep the feet held tightly together. Be sure to land on your toes and utilize the stretch reflex - if you have to gather yourself after each bounce, the spots are too far apart.