What are the best exercises to do before a trailer loading session to set the horse up for success?

Clinton Anderson, Warwick Schiller, and Pat Parelli all emphasize pre-loading preparation, and while their specific exercises differ, the goal is the same: get the horse's mind engaged, responsive, and in a learning state before the trailer is introduced. Clinton Anderson recommends starting every loading session with basic groundwork to establish responsiveness and leadership. Specifically, he works on yielding the hindquarters, yielding the forequarters, backing, and moving forward from a light cue — not because these exercises are directly related to trailer loading, but because they confirm the horse is listening and responsive to pressure-and-release communication before the more challenging ask of entering the trailer. A horse that is already soft and yielding to the halter will be easier to direct toward the trailer than one that has not warmed up at all. Warwick Schiller's approach focuses less on specific exercises and more on the horse's internal state. He may spend ten to twenty minutes simply walking with the horse near the trailer, doing nothing demanding, watching for signs that the horse is relaxed and in a learning state. Licking and chewing, a lowered head, soft eyes, and willing forward walk are the indicators he looks for before asking anything of the horse near the trailer. Parelli's preparation involves confirming the Seven Games are working — particularly the Porcupine Game (giving to pressure) and the Driving Game (moving away from rhythmic energy) — because these are the exact communication tools used during loading. If the horse is not soft on both of those games on the ground away from the trailer, Parelli would not proceed to the trailer at all. He considers that preparation time as time saved, not time wasted, because every minute of foundation work near the trailer reduces the time needed at the trailer.