Getting the six-pack you dream about is not only about doing more and more crunches. To best work your abdominal muscles, you need to work your muscles from all angles. The best way to do this is with core moves that work a variety of muscles within one single exercise. You might think of it like multi-tasking your muscles. Besides giving your abs a complete workout, you will find that you also raise your heart rate which means you are also burning some extra calories.
These moves are best performed following a warm-up (light cardio, at minimum), your regular cardio session, or strength-training workout. Aim to complete the core workout anywhere from 3 to 4 times per week. This is not a rigid program, though. If you can do all of the moves in one workout—do it! If not, pick a few and blend it into your regular exercise program, or pick a few to do each time. Something is always better than nothing.