Winter is a good time to get back to basics. If you are lucky enough to have an indoor arena during the snowy season then you can keep your horse in training through the winter months with flat work and over fences work. A nice way to keep your horse interested in his work is to switch things up. When warming up, don't just go around the outside of the ring, use the whole ring, circles, figure 8's and serpentines will help keep your horse sharp and listening to your leg and hand aids. Also, try moving your horse up and down through its paces by shortening and lengthening its step. A great exercise for this is to count strides at a regular working gait then try to add strides by shortening his step and remove strides by lengthening his step. Over fences work is good too, try doing some gymnastics with bounces to back off the horse that gets a little strong.
If you don't have an indoor
arena, go for a hack. As long as the footing is good there is nothing
like a nice hack in the snow to keep your horse fit for the next season.