1. Shoulders stay level. For the most part, his shoulder are parallel with the ground as he turns and lifts his lower legs. This takes a fair amount of skill, strength, and balance. Start with low hurdles and keep good posture. Then build up from there.
2. Knees stay higher than foot. All good hurdle walkovers should include this technique in order to protect the knee joint. As your swing leg "clears" the top of the hurdle, bring your knee to your armpit to ensure that the knee does not drop downwards as the leg steps to the ground.
3. Weight the back leg more. Notice as he rotates around and swings the leg up and over, he keeps his weight on his back leg that is on the ground. Try not to shift the weight as the swinging leg lowers to the ground and you will have a much easier time completing the drill.