Slalom jumps are very helpful when it comes to building quickness, direction-changing abilities, and ankle strength. To perform a slalom jump you just need to find a line on the ground (or draw one with chalk). Stand on one side of the line with your feet together. Your feet should be running parallel to the line, not facing it. Now you just need to hop back and forth as quickly as possible across the line, moving from side to side. Try to limit the bending of your knees when you perform slalom jumps. Try to keep a rigid form in you legs and use your calf muscles to push you from side to side.
Here is a short video of a guy performing slalom jumps. In this video, he is moving forward with each jump. You can either do it this way, or just stay in one place.
Slalom Jumps Video