Starting with a sitting trot, canter your horse by increasing leg pressure. Learn to canter a horse with tips from an equestrian team coach in this free video on horseback riding.
Once you're comfortable blocking and trotting your horse, it's time to move on to cantering. The most basic way to begin the canter, is to start with a sitting trot. From the sitting trot, we're going to bring the outside leg back. The outside leg is the leg near the rail, in this case, my right leg. My inside leg will stay at the girth, and I'll just keep her bending to the inside, like normal, so right leg back, and canter. At the canter, you want to let your seat be loose, and following the horse's movement. Then, to come back to the trot, I'm just going to lightly apply my Rein Aid, and then if you need to, you can use your voice, and walk.