Other than knowing your individual horse, non-pharmacologic prep is based on choosing suitable horses for the job, consistent training, giving horses adequate time and show experience to learn their job, and having a well trained and prepared RIDER riding the horse.
I think it can be a really hard job to prepare a horse to show competitively under a not-so-great, possibly nervous or clumsy rider who may only ride the horse at shows and doesn't have a partnership with the animal. Horses aren't machines, they are sensitive creatures.
In addition, I think it can be difficult to naturally prepare a hunter for a winning round in the ring of a judge that rewards an overly quiet, robotic round. IMO/E, there are judges that prefer an unnatural level of quietness that may not generally be achieved with training alone in most healthy horses.