We (Mingus and I) are a work in progress, so I can give you a sort of midway report.
One is to know your horse. For all of his orneriness, Mingus is a pleaser. He is smart and willing to learn, and takes great pride in giving me what I want. My yearling Flash is more of a happy-go-lucky sort, confident that whatever he does is good and correct.
Getting a solid whoa is critical, and the biggest problem we had this year. Mingus would stand beautifully at home, but get antsy at a show and want to bury his head in my stomach. We have been working on whoa by walking/trotting/whoa-ing in halter and at liberty -- simply by voice command, up close and at a distance. Once I stand him, I make him hold that position until I release him. I back away, circle him, give treats to the other horses (that's a real test!), and and stand away from him with a loose lead.
I also learned from Liz (Nootka) the importance of maintaining a good pose at all times in the ring, and then really sparking when the judge is right there.
Mingus understood "stand" right off the bat, but it took awhile to position his feet correctly. Since he is AMHR and looks very Shetland, he looks best slightly stretched, and he tends to do this naturally. Remember the old saying with kids of catching them doing something right? When he stands at the fence, he stands beautifully, neck stretched but arched, back legs slightly parked, front legs perfectly square, so I tell him to stand and reward him for what he is already doing. It works like a charm.
As for placing feet, I tell him to stand, then if necessary hand place his feet, all the while saying "Feet." After I position his feet, he tends to not put his weight back on that foot, but Liz showed me the trick of pressing down slightly on that hip so that they distribute their weight evenly. He now moves into the correct position upon command on his own most of the time, and if a leg is out of position, I say "Feet" and he corrects on his own. We're not 100%, but he's getting there.
At one of our shows, a Shetland owner told me that they give their horses treats over the stall gate or over the fence, thus encouraging them to stretch and "hook." This is working well for us, but then our fence is just the right height.
A trick I learned from Amy (Clickmini), is to use clicker training to get them to touch their chin to your hand, and then slowly move your hand back so that they arch their necks nicely. Mingus picked up on this one instantly.
Mingus is such a ham, and responds to the word "BEAUTIFUL!" as if I had said "Here's a wole bucket of grain just for you!" I'm using this to get him to really spark when he trots beside me. He has such a fast extended trot that I think he finds it boring to trot at my pace -- but with "head up" and "BEAUTIFUL," he's getting the idea to turn it on.
I really like playing up on his unique character. He's a very spirited horse, a bit on the hot side, but quick to learn and very bonded to us. I want to harness that energy and make it work for him, and make certain that he always enjoys showing off.
It will be very interesting training Flash -- he's such a cuddly puppy dog that I have to use a different approach, but he, too, is a quick study and very focused. And talk about an extreme change from relaxed, lazy pasture pet to upheaded show stance...and all the while, Thelonius gets treats and kisses for nosing the soccer ball and for just being my darling.
This winter is going to be fun!
I hope this helps just a little bit.