The best exercises for that is flat bench dumbbell flyes with an offset grip and wide dips. For the flyes, when you're lying on the bench, your palms will be facing towards your feet instead of facing each other. Also, your thumb and index finger should be pressed against the inside plate. For the dips, use a wide grip around 32 inches, tuck your chin to your chest and look down at the floor, and hold your legs straight so that your feet are under your face. When viewed from the side, your body will look like a curved line. Try supersetting these 2 exercises for 3-4 sets of 12 reps.