What Simone said, do lots of transitions, and try teaching your horse voice commands that when you do that sound, they'll go immediately. My horse is still green and learning his canter and what the aid is but if I give the aid and kiss he'll immediately go into canter, from halt, walk etc. And he's quite green. And I have a few other voice commands... to slow down, speed up, walk, trot, canter, gallop, halt, stand, etc.
Do some horsemanship to earn his respect and trust. That might make him listen and respond to your cues better.
Practice transitions (walk to trot, trot to canter, canter to halt, etc.) this will help your horse to start listening to what you want him to do rather than them stopping whenever they feel