One of the hardest things to do in tennis is to keep your head still during the swing especially when your body is going in the opposite direction. Some of the best pros such as Muster, Becker, Nadal and Federer are fantastic at keeping their heads still.
People look up because they want to see where the ball is going and they think they need to hurry to get back into position. Don’t worry you’ll have time to leave your head still and recover and get back into position. The concept of this drill is to track the ball as it comes to me, I connect and my head is still, to help with that I look at the bucket or in this case the target. Remember no peeking allowed. If you want to groove this it takes a lot of practise, good luck.