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.
You can learn a lot from competitive powerlifters. But you can also really screw up your progress if you follow their "rules" blindly. Here's the cold hard truth.
Doing this glute-builder in a rack acts as a depth gauge, much like box squats. It keeps your form in check and it makes it easy load and unload plates.