You’ve received some great advice already. We all learn differently, so there is no perfect way to correct form. Here are some of the things that I do, that may or may not work for your situation. For me personally, I like take a few minutes of class time to educate, which reduces (but will never eliminate) my need for corrections later. If I have time, I do 1 and 1.5. If I don’t have time, what seems to work best for me is to demonstrate for about the first half of the time that we’re doing the exercise so my visual learners can get it, then I coach verbally and with touch as my second and third lines of communication.
1) If there’s a particular movement that your students tend to have trouble with, take some time to go over it during your warm-up or right before class.
1.5) My preference for doing this is to allow members to observe themselves in a mirror and self-correct. So, for example, I might have people do a standing side lunge and then I’ll talk through each body segment and where it should be in relation to the others.
2) Verbal corrections first, drawing attention to my own form and addressing the class generally.
3) My weight training classes tend to be 25 people or fewer and I know them, so my next verbal correction would use a name to draw attention and then a short correction from the front of the room – “Nancy, shoulders down and back.”
4) For people that don’t learn well by listening, the next individual cue I would make would be to do correction one on one but instead of touching the client, I’d have the client control whether they touch me or not. For example, if I have a client whose knees are going far forward of their toes in a squat, I’d put my hand at knee height and about an inch behind the front of their toe. Then I’d say, “Don’t touch my hand,” which will make them drop their hips back. If they can’t figure out how to not touch me (most people figure it out on their second rep after they bang into my hand on the first rep), then I’d give the next cue, “Put your hips back so you knee doesn’t touch my hand.” If they over-correct so that now they’re not moving their ankle, I’ll give one more cue – “OK, knee is good. Now, keep the hips back there, but bring the shins just a little forward. It’s like skiing, you have to flex your shins into your boots but keep your hips back.”
5) I touch clients in my weight training classes. As a personal trainer and a yoga instructor, it’s in my scope of practice and I’m comfortable doing it. Here’s the catch. I almost never touch anyone I don’t know; I’ll only touch a new person if what they’re doing will injure them and verbal cuing has failed. Even when I do know them, I will make sure that they can see me coming so my touch is not a surprise. And then I tell them what I’m going to touch.