Do you mean with your hands or with your body?
If your body, try focusing on waiting with your upper body. Think about bringing your shoulders back, or keeping them in line with you leg. Maybe your off balance a bit? Push down hard in you heels to keep you body steady and to absorb any shock from his bellowing canter.
I used to have trouble keeping my hands steady and an old trainer of mine would make me hold the front of my half pad. It was actually harder than it sounds! It really have to think about what I was doing!
"There is something about the outside of a horse that is good for the inside of man." ~ Sir Winston Churchill