1. Have your horse in rhythm so that you can count the canter strides. Count down to "two-and-one-and" will get you to one-half stride before takeoff.
2. One-half stride out, rise in the saddle slightly but DON't lean forward yet. All you're doing is getting your weight off the hindquarters so that your horse can place the hind feet for takeoff. Keep the leg on and light contact on the bit so you don't get a last-minute shutoff.
3. When you feel the horse's hind legs place for the takeoff, rock your balance very slightly forward and let the horse's forehand rise underneath your chest. It's not really leaning forward, more letting the horse come up to you. The bigger the fence, the faster this all happens, and you do wind up kind of throwing your butt up in the air on a big takeoff in order to catch up with Dobbin. But I don't jump the big stuff as a matter of course, no more than 1 or 2 fences 3 feet or bigger on any given day. Big fences are hard on older horses' legs, and you can work on details like approach, turns, pacing, etc. on a 2 foot fence just as well as 3 foot or bigger.
4. You can grab a handful of mane about 16 inches forward of the withers, or you can follow the bit with your hands. When I'm in the field, I do a strong crest release, running my hands well forward, so that the mare has complete freedom with her head and neck to balance. In the show ring, I would keep more of a contact with her mouth, but there the jumps are properly spaced and you're in a confined area and jumping at an easy speed.
Wow, you make it seem so complicated. As an old foxhunter myself I figure that if the horse and I are still alive on the other side of the fence, it was a good jump!
Just kidding. That was a good explanation for her.