Sit on stool or end of bench with dumbbell. Position dumbbell down to side with arm straight. Turn pinkie finger side outward.
Raise arms to side, slightly in front until shoulder height or slightly higher. Lower and repeat. Continue with opposite arm.
Raise toward 10 o'clock with left arm and toward 2 o'clock with right arm. Maintain straight elbow position with elbow pointing outward throughout exercise.
Jobe FW, Moynes DR (1982) describes this exercise to strengthen supraspinatus muscle with abduction in scapular plane (30° anterior to the frontal plane) with glenohumeral internally rotated, AKA "empty can" exercise.
Shoulders should be kept back since scapula protraction can decrease width of subacromical space, possibly increasing risk of subacromical impingement (Solem-Bertift E, et al. 1993).
Also see Dumbbell Full Can Lateral Raise.