2. Twist Crunches
Crunches are standard exercise, but that's because they work, especially when it comes to strengthening your abdominal muscles and your core. Lie flat on your back, hands behind your head, knees bent. “Crunch” yourself up, twisting slightly so your left elbow touches your right knee, then lower yourself back to the ground. Crunch again, this time with your right elbow touching your left knee. Repeat so you do 24 crunches, 3 times.