A guide to great abs has to be the complete package, the handbook for great upper and lower abs without forgetting the obliques.
First, there is the upper abs.
The classic exercise to make this part of your abdomen burn are the ab crunches.
Try varying it up a bit to get the most out of every crunching move, do your crunches while lifting your legs straight while keeping a forty-five degree angle or less from the ground.
You should feel not only the upper muscles working but also your lower abs as the effort to lift your legs makes you contract those leg muscles as well.
Then there are your obliques.
After you do the crunches above, do another set of crunches, but this time bringing one knee closer to your chest, one at a time, alternating sides.
If this does not prove to be challenging for you, you may try bringing your knee towards the opposite shoulder to further engage the obliques and make them work harder.
Finally you should concentrate in exercising the lower abdomen correctly.
The first exercise mentioned helps with working out this area, but you have to put in a bit more effort since the lower abs are the hardest to flatten.
The best exercise for them is to do leg lifts.
Do this beginning with a lying down position and then rising and keeping your legs lift into a ninety degrees position and then slowly put them down until it is just inches from the floor and lift them up again, repeating the same motion.
After doing these exercises, you should feel like your whole abdominal area has been worked out, you should really be feeling the burn.
If you keep at it consistently, you will not just have a flat stomach but also great curves to compliment it.