Lie on the floor with legs straight in front of you, and arms stretched out to the sides, stabilizing. Reach with one arm while you lift the opposite leg, twisting and bringing your shoulders off the ground until you touch. Do 15 reps, then switch sides.
Sit on the ground holding a dumbbell on both ends. Lean back about 30 degrees while using your abs to stabilize. Take the dumbbell and twist from side to side. To make it more difficult, raise your toes off the ground. Do this for 30 seconds.
Start in a classic plank position. From here, bring your knee in and across to the opposite elbow. Alternate sides quickly for about 30 seconds. Keep your abs engaged and make sure your hips don't drop. Repeat 3 times.
Sit with your arms bent and braced behind you and your legs bent in front of you. Raise your toes off the ground and bring your knees up to a 90 degree angle. Then lower back towards the ground, with letting your toes barely kiss the ground before bringing them back up. Do this for 30 seconds. Repeat 3 times.