It hardly depends on what do you want to do with your foal in the later times. Do you want him to a reining, barrel-racin ghorse or would you like to do some classical dressage?
Usually we do this way
First 4 months: the horse learns to carry your weight. Many walk, many trot, only a few canter. In the first months the speed of the gaits depends only on him, I usually don't try to make him faster or slower. The hardest thing I ask from him is to keep one tempo chosen by himself for a longer time. Many countryside riding.
Second 4 months: more time in the school. Begin arcs and circles. Begin to get him used to your weight and leg directions. By giving him a very stable and calm hand, he will get the bit and work on the bit correctly. It's an important thing because if you miss it, your horse will not go on the bit, you will have many trouble with him. Shy horses like go beyond the bit, harder ones go against the bit.
Third 4 months: Getting his balance upper by making him working with his backward legs better. When you start to work with a foal, the highest point of his backside is the top of the bottom. After 12 months the highest point must be the wither. You can reach it only when he is on the bit. You must help him with your legs to warn him about using correctly his back legs. Use it when you have a feeling that you are sitting only on his wither and his back legs are somewhere far-far away from you...