To perform an Arnold press, sit tall on a chair or bench, your feet planted shoulder-width apart, your core engaged. Holding a dumbbell in each hand, bend your elbows and position your hands in front of your shoulders, your palms facing your body, as if you just performed a dumbbell curl. This is the starting position.
In a fluid, controlled motion, press the dumbbells up over your head, and as you do, rotate your palms inward, then forward as you complete the press, so that at the top of the motion, your arms are extended and your palms are facing outward, away from your body. Reverse the movement as you bring the dumbbells back to your shoulders, rotating your palms in, then toward your body as you lower the weights.