Today we're doing what I refer to as Jumping Lunges, and if you know how to do a lunge, then a jumping lunge won't be too hard to explain. (If you're unfamiliar with lunges, click here to read a how-to on lunges.)
Try this exercise 3 times/week, completing 3 sets of 12 reps (6 per leg), resting 90 seconds between sets.
Start with arms at your side. You can have your hands on your hips for balance to begin. Step forward with your right foot into a lunge position. Lunge down, bringing your left knee almost to the ground and making sure your right knee does not go past your right toes. (Your right shin should be parallel to a wall.) One way to make sure you are lowering yourself correctly is to watch yourself in a mirror; your spine/torso should be moving straight down with absolutely no side-to-side movement.
When you've lowered yourself to the down position, jump up by pushing through your right heel and left toes, switch positions with your legs, and land softly on your feet. Now your left foot should be in front of you and your right leg should be behind you, again in a lunge stance.
When you do your "soft landing" after you jump, do not stop moving. Immediately (but with control) lunge down, and then jump again, switching the position of your left and right legs. Control your landing so your feet land softly and your movement to the down position of the lunge is also controlled and smooth.
One main purpose of this exercise is to use your core (abdominal and back) muscles to control your movement so you're not falling to either side but you are still maintaining a fluid motion while lunging, jumping, landing, lunging, jumping, landing.