getting stronger is key, if your max on the bench press is 225 lbs, your chest will be much bigger by the time you bench 405 lbs, but make sure your front delts and triceps don't get too strong, otherwise you'll be like those bodybuilders who can bench a lot but they have huge triceps and delts, but their pectoral muscles are nothing special. Good posture is key, practice the vacuum pose all the long, and stand straight, like Arnold, it will stretch out the pectoral muscles. Remember, having huge arms means nothing if your chest is small, the body has to grow in proportion (perfect proportions, or the closest thing to perfect proportions is Arnold)