Okay, I agree with Trainer 2. You need start him off correctly, or the same way you are going to always ask him. You don't want to confuse him, or teach him one way and then have to re-teach the other way, for it will be more difficult for him.
When I am teaching one showmanship, I start them all off the same. Hold your lead in your right hand ( that is your controller, think of it as your joystick, from games years ago...ha ha.) But that is how you cue for all movements. To start with you will over exaggerate your upper body along with your hand, and then the goal is to eliminate the body and only use your hand for your cues. So, for example, when I am teaching one for the first time I start with walk to stop, over and over and over again. I extend my right arm forward, lean forward with my shoulder, but my feet do not move until the horse moves, you want the horse to take the first step forward and then you follow. You are teaching your horse to follow your hand! So, arm is forward, shoulders are forward (over exaggerate) and then cluck until the horse takes a step forward, then you follow.
Biggest key is to keep your arm forward the entire time you want the horse to go forward, no moving the elbow until you want your horse to stop. I close my elbow, straighten or over exaggerate back and say whoa. Continue until the horse follows your hand every time. Then when you ask for your trot, I start from the walk with a young one, I do the same thing as for the walk, but over do your shoulders and upper body forward, and think "follow the hand" forward into the trot. Again, do not start running and get in front of the horse, for you want them to follow your hand, I use a kiss for my trot and cluck for my walk with a baby. You have to make the cues different so they understand, but very easy for them to understand. If he won't trot, ask a couple times, and then very gently, do not do it hard, swing the left hand with excess rope and gently swing to his side, behind his shoulder while you continue to ask for forward, do not change your right hand or shoulders forward of he will not understand what the added "forward" is for.
If you need any more help, please feel free to send me a message, for it is such a long post as how to really start one for showmanship.
Hope that helps! and by the way....showmanship is my favorite class!!! so work hard and you will have a blast when you get there!