Schedule your core workout three days a week. Give your abs and obliques a day off in between each workout so they have time to heal and recover.
Complete two sets of each exercise, with each set consisting of 10 to 25 repetitions.
Perform the bicycle crunch during each workout. The bicycle crunch was found in a 2001 study by the American Council on Exercise to be among the most effective exercises for targeting both the abs and the obliques. Lie on your back on an exercise mat with your feet up off the floor and knees bent and your hands interlocked and placed behind your head. Crunch up and twist to the left while you simultaneously bring your left knee up to your chest so your right elbow and left knee meet over your torso. Lower back down and twist the opposite direction on the next repetition, bringing your left elbow to meet your right knee.
Incorporate straight-legged crunches into your workouts. Lie on your back on the exercise mat with your legs straight and held up vertical. Hold your arms up and crunch toward the ceiling, trying to touch your shoelaces with your fingers. Control your shoulders back down to the floor.
Complete oblique crunches. Lie on your side on the exercise mat with your legs stacked on top of each other and your knees slightly bent. Place the hand of your top arm behind your head. Crunch up toward the ceiling by bending at your torso. Hold the top position for a moment and then lower back down. Finish all the repetitions on one side before flipping over and performing the exercise on the other side.