Instructions
Take the horse out to an open field or to an arena that has long sides. This will enable the horse to pick up speed and maintain it for multiple strides without having to go around a corner. The longer the horse can move in a straight line, the easier and more enjoyable it will be for the horse until it learns how to balance.
Squeeze the horse's sides with both calves to ask for the trot. Since the horse is just being trained to trot under saddle, it may take more pressure than the rider is accustomed to using. Make sure that there is no pressure on the horse's mouth by the reins. Cluck or make kissing sounds to help urge the horse on. If the horse does not trot, but increases the pace of the walk, reward the horse by giving it relief from the leg pressure. Wait a moment and ask for the forward motion again.
Praise the horse with the voice or a pat on the neck as soon as the horse begins to trot. Encourage it to keep trotting by clucking and keeping the leg aids applied. If working in an arena, settle into the saddle and let the horse walk before it has to negotiate a corner. Repeat the process of asking the horse to trot and then walk until the horse is comfortable and responding readily to the aids.
Gradually increase the time that the horse trots. Add corners and direction changes with each consecutive session as the horse becomes fitter and more balanced. Post the trot rather than sitting it to make it easier for the horse.
Ask the horse for trot to canter transitions rather than walk to canter transitions, which are significantly more difficult for a young or green horse. Decide which lead you would like the horse to pick up. For the left lead, apply the left leg at the girth and the right leg behind the girth and squeeze. Do the opposite for the right lead. Maintain leg contact while clucking to urge the horse forward into the canter. As soon as the horse picks up the canter, stand in the two-point position to allow the horse to move freely without being hampered by the rider's seat.
Praise the horse for attempting to canter even if it cannot physically maintain the gait. If the horse breaks to a trot, slow the trot and ask for the canter again. A horse who is just learning to make the transition may need to run into the canter from a very quick trot until it learns to balance and understands what is being asked of it.
Slowly increase the number of strides the horse maintains at the canter. Allow the horse to go around corners, but do not attempt any tight circles until the horse has learned to balance itself --- and the rider --- without speeding up the canter or breaking to the trot.
How to Train a Horse to Trot & Canter
In order to train a horse to trot or canter, the horse must have been previously started under saddle and readily accepting of having a rider onboard. The horse needs to have a basic understanding of leg, voice and hand aids before it is safe to teach it to trot and canter.