Your deltoids are the biggest and strongest muscles in your shoulders, and are made up of front, back and middle sections. The middle deltoid muscle is the one you use to abduct your arm -- that is, move it away from your body. Exercises to tone and strengthen this muscle will help give your shoulders their characteristic, defined shape.
The Arnold Press
This exercise gets its name from the man who created it, Arnold Schwarzenegger. You can sit or stand to do it, but regardless of the position you choose, keep your back straight throughout the exercise. Take a dumbbell in each hand and bend your elbows so the weights are positioned in front of your chest, palms facing in, and your elbows pointing down towards the floor. Raise the dumbbells straight up over your head, turning your wrists inwards as you do so, so your palms face forwards at the top of the movement. When the weights are raised, keep your elbows slightly bent to avoid locking out the joints. To lower the weights, rotate your wrists back so that you finish with your palms facing in towards your chest.
Reverse Lateral Raises
Sit or stand with a dumbbell in each hand and raise your arms out to the sides to shoulder height. Keep your palms face up and your elbows slightly bent. Then engage your shoulder muscles to lift the weights up so they meet over your head. Slowly lower your arms back down to shoulder height and repeat the exercise as many times as you can while keeping the movements controlled.
The starting position for this exercise is standing with your feet shoulder-width distance apart and your arms by your sides with a dumbbell in each hand, palms facing inwards. Raise both arms out to your sides at the same time, stopping when they reach shoulder height. In the raised position, the backs of your hands should be pointing towards the ceiling. Hold for a second before lowering back down to the starting position, finishing with your palms facing in towards your thighs. Repeat as many times as you can while maintaining proper posture and control of the movements.
Stand with your feet about shoulder-width distance apart and a dumbbell in each hand. Start with your arms straight so the weights are resting against your thighs and your palms are facing inwards. Bend your elbows up and out to the sides and lift the weights up to shoulder height. Hold for a second then lower back down and repeat. In the raised position, try to keep your elbows slightly higher than your hands.