Starting in trot on a 20m circle to the left, establish a working trot with good energy and a steady bend to the left. (This is the body of the snowman.) As you cross over one centerline, make a 10m (or slightly larger) circle to the right. (This is the head of the snowman.) After one smaller circle to the right, come back onto the 20 m circle to the left, and ask for a canter right away.
This exercise is helpful for horses at any level. For very young or green horses, it is a helpful way to get the correct lead in the canter, if the horse struggles to pick it up.
For a Training/First Level horse, this exercise is especially helpful to ride in the direction that the horse tends to bulge its outside shoulder. If your horse tends to bulge the outside (R) shoulder when tracking LEFT, riding a smaller circle to the RIGHT lets you bend the horse RIGHT and push him out off your RIGHT leg. Then as you come back to the 20m circle LEFT, he should be more respectful of your RIGHT leg and not bulge out as much. This will help to get a better canter depart, because you can keep him better balanced “across” his shoulders.
For a more advanced horse, this is a great way to practice multiple canter-trot-canter, canter-walk-canter, and flying change transitions to build strength and longitudinal suppleness through the back, while the frequent changes of direction and smaller circle improves lateral suppleness.
Start the exercise the same way, but then ride a transitions just before the next centerline and repeat the smaller circle to the outside in trot or walk, then back to canter on the 20m circle, then back to trot or walk before the next centerline, and onto a smaller circle to the outside, etc.