once or twice a week just like any other muscle, upper: hanging leg lifts, decline crunches, cable crunches, and whetever the gym offers. Lower: lay down leg lifts, and i use this machine at the gym. as longas u tighten the muscles u want worked and u feel them burn. I also do side dips with weights. Running and cardio is also very important, u need to get rid of that fat to have abs.