Two things I’d recommend:
I think the human mind is only capable of learning a few new things at a time. By the time you teach someone how to stand and hold the bow, you’ve probably reached that limit, but in order for them to actually shoot an arrow, you have to teach them a few more things than that. Maybe that’s why in the eastern tradition of archery, all they are allowed to do for the first year is draw the bow without shooting it. Anyway, try to limit the things you tell them during the first lesson to no more than a half dozen things, which is already too much.
Learn how to identify faults by watching someone shoot. This is a real talent that Arne has, and I am still learning. Watch some videos that Arne has evaluated, and try to guess what he is going to say before he says it. Any good instructor can size up a student after watching him shoot just a few shots, and knows what one or two things he is going to work on that day, even though there may be many other things that could also be improved.