Crunches work out the upper ab region a lot faster then sit ups. In order to do a proper crunch place your hands nice and gentle on your chest and let your ab muscles and back do the work. Don’t go to fast, go nice and slow, feel your abs burn. The great thing about the crunch exercise is that you really feel your abs burn, it is a great feeling and lets you know that you are working out those abs.
Do 3 to 4 sets of these workouts every other day. Its a good idea to take a break every other day. Taking a break between workouts lets your muscles rest and build strength. All tho some hard core muscle builders disagree with this, but I believe that they have been working out the same muscles for so long that they no longer need to rest. So please do keep that in mind. For the lower abs you can choose from bicycle crunches, the v holds, or some good old fashion ab pull ups. I will put a lower ab exercise video below that will go into great detail that will show you how to do these lower ab workouts with proper form.
Example Crunches workout. Thanks nailaray.com