Horses are so sensitive to the slightes movements in the human body, that we actually end up talking away their sensitivity to our cues (commands)by micromanaging them. I notice this alot when we ask the horse to stop and go especially. Lets for a minute talk about energy. When riding a horse we should use more energy the faster that we them to go and less energy for the slower we want to go. I of en see people kick their horses or using a crop when wanting to go faster, but they are just sitting natural on their horse. For horses they feel what your energy level is and they will be great at going to the pace of your energy, but often so many people don't understand how sensitive they are so they use a crop to get them to go, therefor the horse now loses that concept.
Like when I ask my horse to go from a halt, I lift up my body energy and for trot more energy, and canter alot of energy. Once you start teaching this to horses, it becomes so much easier to focus on other things than having horse horse go or stop. Also something else that works is if when going down from the gait, that you sigh. This tells the horse oh relax a bit OK. The more heavy the sigh the more stop you should have. Try it and see if this works.