Crescent reps, demonstrated by Tamal Dodge, co-founder of Santa Monica's Yoga Collective and the yogi behind Element's "Hatha & Flow Yoga for Beginners" DVD, are a great way to tone the legs and get the body warmed up for other exercise.
What it does
The movement in this pose gets your heart rate up at the same time you're working your glutes and hamstrings. It also challenges the center of balance, which indirectly works the abdominal muscles.
How to do it
Start in a standing forward bend, with your hands touching the mat in front of you (or as close to the floor as you can get). Step your right leg back 3½ to 4 feet so you're in a runner's lunge with your left knee bent and right leg extended on the ball of your right foot. (The taller you are, the wider your stance should be.) Slowly bring your hands to your sides, so your body forms a straight line from your right foot to your head. Inhale and raise your hands and your upper body until they form a straight line to the ceiling. Exhale and slowly lower the arms and upper body until you are back at your starting position. Once you're finished with 10 repetitions, step your right foot back in standing forward bend and switch to the other side.
Start with 10 repetitions on each leg. Work up to two sets of 10.