[header] How to do sit ups [title] Start by lying on your back with your knees bent. [step] Sit ups work best if you do them on a soft surface, such as a mattress. Keep your knees bent at a 90-degree angle, with your feet flat on the floor. 
[substeps] You may be more comfortable if you lie on an exercise mat while you're doing sit ups. [title] Put your fingertips on the back of your ears.