Support yourself by your forearms on a roman chair. Lift your knees towards your midsection. Use your abs to pull your legs up. Rotate your pelvis foreward to really crunch your abs. Exhale on the way up and inhale as you bring your legs back down.
Here are a few suggested alternative exercises:Ab CrunchAb Crunch ObliquesBall Crunch TraditionalDouble CrunchDumbbell Side BendsLateral Bend with Barbell