Position
Stand with your feet just wider than shoulder-width apart. Bend your knees and hips, with your trunk between 45 and 75 degrees in relation to the floor. Maintain a natural arch in your back. Keep the weight over your ankles. Place one hand on your hip, and in the other hand hold the dumbbell perpendicular to your body, your arm straight down, and your elbow pointed out and slightly bent. Pull and hold your shoulder blades tightly together throughout the exercise. Begin with your arm slightly out so there is some degree of gravitational pull on the dumbbells.

Technique
Contract the posterior deltoids of your shoulder. Bend your elbow and pull your arm out and up until your upper arm is approximately parallel to the floor, forming about a 90-degree angle. Hold and continue to contract your posterior deltoids. Keep your arm relaxed, elbow pointing up, and scapulae retracted. Slowly lower your arm back to its original start position, keeping your scapulae retracted and tension on your posterior deltoids. Repeat.