Three elements: diet, sleep and posture.
If you are looking for exercises somewhere in the equation, it’s there, but training will never outweigh these very important elements of your lifestyle.
Obviously, diet is the major culprit of a potbelly. However, it doesn’t stop at eating well. Yes, a good diet will help, but the food of some might be the poison of others. Some can tolerate gluten, others don’t. Some people, even when dieting, seem to have some kind of little pot belly, or just look inflamed. If that is the case, avoid everything that contains gluten for a couple of weeks and see if your little pot belly goes down.
Sleep is another issue that most people underestimate. No sleep, no recuperation. Most will train harder, but not necessarily eat accordingly, which puts a stress on the body. When cortisol levels are elevated, sleep issues start to appear. A delicate balance between training and dieting needs to be achieved and maintained for an extended period of time to get great results.
Last but not least, posture. When the abs are weak, it can create a very bad posture. Going from tight psoas and lower back to weak hamstrings and really bad neck problems. When the pelvis tilts forward, it gives the look of a protruding belly. Training the abs properly is great, but the rest of the body needs to follow, such as hamstrings, lower and upper back muscles; everything. So it’s not by doing 1000 crunches at night that you’ll get a flat stomach, train the body as a whole.