Sample cardio exercises are the stationary bike and treadmill. If you decide to use a treadmill, brisk walk instead of running. What works for someone else may not work for you. You must experiment with each to find which is best for your individual body type. The answer to this question is widely debated by experts.
Opinions vary from training abs every workout, to once a week.
The key thing to remember is that everyone has a different body type. The truth is, you must test every option to find which method works best for your body.