Nothing wrong with sticking to the classics. This old favorite is easy to do on your bedroom floor. Lie on your back with your knees bent and feet about 12 inches from your butt. Put your hands behind your ears. Focusing on your core muscles, lift your head and shoulders and raise up until your head, shoulders, and back are off the floor. Keep your belly button pulled in. Lower back down to complete one rep. Perform 15 reps.