I don't have a ton of experience with training to square up for showmanship, but hopefully I can at least give you a good start. And someone more knowledgable can fill in the details.
The main idea is to work with the feet in the same order with the same cues every single time = consistency.
And it is important to always practice in the same halter and leadrope setup that you show in so that the cues are the exact same.
You always want to get the back feet set up first. Whichever back foot is in the best position when you have stopped, leave it be. Instead, adjust the other foot to match it. Put very slight backward pressure on the leadrope and angle the pressure either to the left or to the right, based on which back foot it is you want to move (ex: pressure to the back right will cause the horse to move the right hind foot backward).
Or, if you would prefer to move that foot forward to match the best-positioned hind foot, you would put slight forward pressure on the lead, also at an angle to match the foot you want to move forward.
When you have the back feet set, leave them alone!
Now work on the front feet. Instead of doing backward and forward pressure cues (which are going to be reserved for moving the hind feet only), do side-to-side pressure cues for the front feet. This lets the horse know which set of feet to move.
Like we did with the back feet, pick the front foot that looks the best positioned and leave it alone! Move the other foot to match it. So if you need to move the right front foot, pull the lead to the LEFT because that will put the horse's weight on their left front foot in order to free the right front foot to move. Once that foot is "free" to move, you can use slight backward and forward pressure to move it accordingly. But the important cue for the front feet is that initial side-to-side cue to shift their weight.
When the front set are set, leave the horse alone! Often it is best at this point to have a single cue word for your horse such as "whoa". This is their cue that "Hey, we are set up so don't move!" and they know they no longer have to move their feet around.
It is best to keep teaching sessions short and frequent. It would be much more effective to work on this 10 minutes every single day, rather than to work on it for a whole hour only one day a week (where the horse just gets bored).
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.