Lie supine with your back on the floor. Bend your knees. Your feet can be flat on the floor, or you can keep them suspended in the air during your crunches for a little extra crunch. Place your hands behind your neck or head, with elbows pointing toward opposite walls. Your head and neck should be resting on your hands. Note that it can be tempting to move your head forward (tucking in your chin to your chest) because it makes you feel like you’re lifting further, but you’re not. It’s a bad habit that increases your chance of getting injured. Always try to keep looking up at the ceiling when you are crunching. Now lift your shoulders towards the ceiling contracting your abdominal muscles, and pause for a moment at the peak. Return to supine. It is very important not to lift your entire back off the floor, as this can cause strain – keep your lower back on the floor. Repeat.
If you have your hands behind your head or neck, don’t let your elbows come together. Keep them level with your ears. Letting your arms close in around your head encourages your head to tilt forward. Exhale and contract your abs as you go up.