This document provides instructions for doing effective sit ups. It recommends getting into the proper form by lying on your back with your head up, arms straight along your body, legs bent with feet flat on the ground. The ideal position involves tightening your core and crossing your arms over your chest. To perform a sit up, lift your head and shoulders while keeping your toes and heels planted, using your bent knees as a guide to look at. Pull your torso up to a 90 degree angle without letting your back touch the floor, then lower back down slowly. Repeating this motion while maintaining form will work your core muscles.