All spins happen on one leg. This point is obvious with one-footed spins (sometimes called figure skater turns or pot-stirs). However, even traveling spins, like barrel rolls, can be broken into traveling motions (in which the center shifts from one foot to another) and rotating motions (during which the center remains stationary over the supporting foot). If you try to combine both rotation and traveling, you will be off balance and fall—either onto your new foot, or onto the floor. Thus, one of the keys for spinning effectively is being able to keep your center balanced over a single leg.
The Drill: With good posture and nice turnout, balance yourself over the ball of your foot. When you feel steady, lift the other leg slightly off the group (the toe should be just skimming the ground) and touch the free foot to the ankle of the supporting foot. Hold this position for at least 30 seconds, then switch feet and repeat.
As you are balancing, pay attention to how your body shifts in order to remain balanced. If you are rocking between the ball and heel of the supporting foot, concentrate on keeping the heel ever so slightly off the ground. If you are rolling towards the outside of your foot, focus on keeping your weight inside. You may find it easier to balance by softening (not bending) the supporting knee.
Throughout the drill, monitor your posture. If your chest is collapsing or if you are rounding your shoulders, you will be less stable and will have a harder time establishing an axis of rotation during the dance. Keep the shoulders down. Your chest and head should be up, as if someone had attached a string to your head and the front clasp of your bra (guys, use your imagination) and was lifting you up. Your core should be tight; work those abs!
The beauty of this drill is that it can be done anywhere. Put in 30 seconds of balancing on each leg while you brush your teeth in the morning, another 30 seconds when riding the elevator at work, and 30 seconds while washing your hands after using the bathroom. This drill is much more effective when done for a minute here and there, several times a day, than trying to do a single 10-minute balancing session on the weekend.
Bonus Variations: You can do a number of things to increase the difficulty level of this drill. Try holding your arms steady instead of using them for balance. Change your height by bending your supporting knee and then straightening it while on one foot. Move your free foot to different positions: crossing behind the supporting ankle, on the side of the lower leg with the free knee pointed out, extended out in a rondé line. For the really balanced, try standing on one foot with your eyes closed.
Life Bonus! Improving your balance is one of the skills that translates directly from dance to life. One of the most important preventative measures someone can take as they age is to focus on improving their balance, because a lack of balance is responsible for a huge portion of injuries in the elderly. Balance exercises are commonly prescribed by doctors, rehab therapists, and other medical professionals because balance is such an essential skill for warding off further injury. So, develop that stability!