Vary Your Grip to Fully Develop Your Pecs
The key to building a massive, muscular and well-defined chest is not necessarily poundage. The real key is to attack your pecs from a variety of angles.
To accomplish this, be sure to strategically use barbells, dumbbells, cables, and machines in a variety of positions (flat, incline, decline).
The worse thing you can do is to do the exact same exercises in the exact same manner workout after workout. You muscles will very quickly adapt to your routine and progress will stall.
One subtle change that you can easily do to help build a full chest is to constantly vary your grip width on all barbell chest movements.
To emphasize your inner pecs and carve out solid definition, move your grip closer together (about 12 to 14 inches apart). Widen your grip to stretch the pecs and hit the outer area of the chest. Even subtle changes in grip can lead to significant progress.