Dude,
a 6 pack is built in the kitchen not in the weightroom. Eat clean, turn the fat that is covering your abs into muscle.
As for lifting: Your abs are just like any muscle - you can overexcercise them giving you the opposite result of what you are looking for. Lift them like any other muscle group - use weights, keep your sets/reps/number of exercises in check.
Eat clean, eat clean, eat clean. They will show up soon enough.