At 3 day events, I often see people practicing the jog repeatedly. The horse gets more and more stiff, gets held, and sometimes fails to pass. For many horses, I think there is a better way to prepare, and pass the jog:
Step One would be a thorough sports massage before the jog. I often combine this with cold laser in spots that are especially tight. The cold laser also helps release calming endorphins when used on strategic points on the head and face.
Step Two would entail a long walk. The walk uses all muscles without using momentum, so it is an excellent warm up. Walking also reinforces the body balancing work that was done during the massage.
Step Three would be to skip the trot and go directly to canter. This could be done on the longe line. Just a few circles in each direction would make a huge difference, as canter is the gait that lengthens all the muscles. (Trot is the gait that shortens the muscles, so continuing to practice the jog will make the horse appear more and more choppy.) Canter lengthens the back muscles, which is so important for every breed, but especially thoroughbreds that tend to shorten up when excited.
I hope these ideas are helpful to all of you this show season. Let me know how it goes!