Abs become more visible when you reduce your body fat %, which you can do by achieving a calorie deficit, and/or increase the size of the muscle, through training. The energy you consume - resting metabolic rate (how much energy your body requires doing nothing) - thermic effect of food (how much energy to digest food) - physical activity expenditure = energy remaining If the energy remaining is negative you lose weight, which will come from fat if you continue to stimulate your muscles through training (giving your body a reason to keep them around). Next up, increasing the size of them through training. The abdominal muscles are no different to the remaining muscles in your body, so usual training principles apply. They are, however, activated for a large portion of the day, so are accustomed to a high work load, therefore training them 2-3x per week will be optimal. You gain muscle in a calorie surplus (when the energy remaining in the equation up there is positive). So in order to make your abs grow, you want to train them in the 12-15 rep range during your muscle gain phase. If you only train your abs when you're losing fat they will not grow, and hence you will continue to require a low body fat % for them to be seen. Simple.