To balance your horse so that both sides of his body are equally relaxed and responsive, you’ll spend two-thirds of your time working on his bad side (the side that is stiffer, pushier or more reactive), and one-third of your time working on his good side.
For instance, if your horse is spookier on his right side, then you’ll want to spend two-thirds of your time desensitizing that side of his body. Or, if he’s really stiff when you ask him to flex his head and neck to the left, spend two-thirds of your time practicing the exercise on the left side of his body.
Eventually, both sides will even out so that you’ll have a calm and respectful horse whether you’re working on his right side or left side.
You’ll find that the horse’s good side and bad side will switch on and off. Once you have him desensitized well on the right side, he might be worse on his left side and vice versa. It’s always going to be a bit of a balancing act.