Two useful exercise to have steady hands. One is holding the crop with your thumbs the other is bridging the reins. I find this really useful for riders who have tendency to ride mostly on the inside rein and who pull the inside rein. The main problem here that they are not aware of it (that they pull the inside rein !) so the fact of telling them not to pull the inside rein has no meaning. This exercise obliges them to have the right contact and therefore the horse comes on the bit naturally. The right feeling of the contact than can be memorised thanks to the memory of our cells !