Not everyone can afford a trailer, to practice with, but I try to make a makeshift area, as big as a trailer, like a little room and have my horse follow me in. This is where he gets a treat.
Great advice. I like the part about teaching your horse to relax on cue. I do that literally. I say "calm" and my horse (and my dog) knows that everything is okay and he doesn't have to worry. It's especially handy in a potentially dangerous situation.
While there are a few good points in this article, I will never lead a horse into a trailer. Safety for the handler is as important as it is for the horse. Going ahead of the horse places the handler in a no-win situation if that horse jumps forward for any reason. I teach my horses and instruct my clients to drive the horse into the trailer, eventually having the horse load and unload with a light pressure or by verbal command.