The best exercise to work your lower abs is the crunch. This can be done by first laying down on a flat surface that does not move much when you are lying there. Next, raise your legs up under you so that you are looking straight up at the ceiling. Now lift your buttocks off the ground and crunch them as tightly as you can while concentrating on pushing your lower abs out as far as possible.
The final choice for working your lower abs is to do a vertical jump. This can be done by jumping up as high as you can from a flat surface. This is one of the harder workouts for the lower abs, so you may need to use a spotter for safety. Be careful not to overdo it though or you may find yourself getting hurt.
The best exercise to work your lower abs is by working them out in small sets. In each set you should be able to focus on an abdominal muscle group for about 30 seconds. It is important to be consistent with your routine so that you do not become frustrated. If you find yourself having to stop every half an hour or so, then you may have to adjust your workout so that it is more effective. Also, when you do these types of workouts be careful to not let your body sit still.