If you're looking for training your abs seriously, try hanging leg raises. These will really hit the lower part of your abs and train your grip strength at the same time, so get ready to be suprised how hard this will get after a couple of reps. If you can't do l pull ups or you just want to stick with ab training, then this is the best thing you can chose. You can use variety of grips while holding the bar but overhand grip is proven to be the most comfortable. Wide grip is also great, as it reduces the unintentional swinging and kiping. Your 6 or 8 pack abs are waiting for you to earn them, so no excuses and go grab that bar and lift your legs up!

L pull up is a great exercise that will not also build your upper body, but will also hit your abs like a truck. It's not an easy exercise, it requires a lot of abdominal strength and should be performed as slow as possible. Isometric contraction of your abs will pay out tommorow in sore muscles. If you can't perform this exercise, then try something different like l hang or hanging leg raises. If you can easly do plenty of l pull ups, then kick it up a notch by mixing the exercise with different kind of grips or grip widths. I recomend wide grip, overhand, l leg raise for a killer workout.