Perform decline bench presses. Lie face up on a decline bench, so your head and torso is lower than your legs. Grip a barbell with an overhand grip (palms facing up), slightly wider than shoulder-width apart. Bend at the elbows, slowly lowering the weight until it almost touches your chest. Extend your arms, pushing the weight directly upwards until your arms near full extension. Repeat. Keep your torso rigid and avoid the temptation to arch your back to assist the lift.
Perform dips to target the lower pectorals. Mount the dip bar with an overhand grip (palms facing inward). Slowly lower until your chest is lower than your shoulders -- you should feel a stretch along your outer and lower chest. Extend your arms forcefully to lift your body back up until your arms are fully extended and repeat.
Perform decline chest flies to target the central, outer and lower pectorals. Lie face up on a decline bench. Grip a dumbbell in each hand with an overhand grip. Bring your hands together directly above you, palms facing each other. Keeping your arms slightly flexed, lower the the weights laterally keeping them perpendicular to your body. Once you feel the stretch across your chest, forcefully bring the weights back together above you. Repeat.
Perform pull-overs. Lie face up on a flat bench. Grip a barbell or EZ curl bar at shoulder-width with an overhand grip. Extend your arms above your head and lock your elbow in a slightly bent position. Slowly lower the weight behind your head as far as you can, feeling the stretch in your lower chest and upper abdominals. Forcefully reverse the movement, bringing the weight back up to the start position before repeating. Select a lighter weight and perform 20 or more reps to build definition in the lower pectorals.