What am I allowed to do with my hands?

BILL– I’m assuming I should confine my answer to dressage-related activities. Even so, my answer would be different if we are talking about in the show ring, best case scenarios when you’re schooling, or some of the exigencies which arise when confronted with impenetrable inherited tangles.
Let’s begin by agreeing that it is OK to use your hands. However, at all cost avoid random, habitual niggling. Anything you do with your hand must be on purpose and carry a message. And generally speaking it should be as a modifier to a primary aid which began with your seat or legs. Nor should it be used in a backward direction (other than when you are in survival mode). Non-allowing – yes. Pulling – no! Often when you think pulling is the solution, a greater push to that same non-allowing is a better choice.
Remember, your hands have some things to say, but in the context of the rest of your arms. Your elbows must remain elastic, and your forearms must be soft. “Your forearms belong to the horse!” Imagine that the reins continue through your hands and up through your hollow forearms to connect into your elbows and back. At the same time, as I wrote in DRESSAGE Unscrambled quoting Rosemary Springer, “Quiet hands are not dead hands.” An inert, non-communicating hand just allows your horse to lean on it.
Another issue is hands which stay too wide apart. I’ve been known to say, “Don’t push the wheelbarrow. Imagine you’re strangling the barn cat.” Not so much in the show ring but sometimes with a greener horse, it’s OK to open a rein but hardly ever both at once. But immediately after you use it, put it back where belongs. Don’t keep it wide.
As for those extreme cases, if I have to describe to you what to do, you probably aren’t ready to be doing. Keep in mind that your hands may need to be corrective, but try, try, try not to let them become punitive.