To improve performance in court sports, like basketball and tennis...
Lateral speed steps
Stand on a 6-inch box. Quickly step one foot and then the other off to one side, and bring them back up quickly, one at a time. Repeat to the other side. Do this as many times as you can in 60 seconds (and aim for at least 1 rep per second). Rest no more than 5 minutes, and repeat 1 or 2 times.
Bonus: Step faster to work harder. Keep your upper body relaxed and upright, and use a box that's about hip width.
For at home or on the road, when you're without equipment...
(Learn six more ways to stay fit on the road.)
Perform the following four exercises as a circuit, and repeat twice. Do one for 20 seconds, rest 10 seconds, and then move on to the next.