When riding as I make a transition I do the voice command as I do it and as the horse gets more responsive I ask for the command less until the horse fully listens to my voice
Hope this helps
Your horse needs to understand the command to respect it, once they understood they will do as you ask
Use one word regularly whenever you want your horse to do whatever you want them to do.
Think about lunging. First thing you do before you ask your horse to go into trot or canter you say it in a specific tone then if it doesn't react straight away you use your whip and repeat the word until the horse goes and does what you want it to do.
Do the same with everything else. Be patient.