This is a great movement to use as a warm-up because it activates the nervous system without overly fatiguing the body. It also teaches you to jump with a weight in your hands, as with Olympic-style lifts.
The movement with the legs should be very fast and explosive. Use a powerful hip action.
The arm with the dumbbell should stay close to the body as it rises.
Remember, while you do pull with the arm, it's the movement created by your lower body that gets the dumbbell overhead.
The boneheads in your gym only know one way to make an exercise tougher – add more weight. That's why boneheads never build more muscle, no matter how long they work out. Our resident Scotsman knows some remedies.