The article linked below is oriented toward self propelled spray rigs, but a lot of the points are valid for our tractor mounted models as well.
The big point is to make sure that you clean your sprayer thoroughly before putting it up for the winter. The article points out that you don't want to be leaving pesticide mix in the tank (does anybody actually do that?), but you should also really clean up the tank before putting it away. The article mentions a triple rinse, I would go beyond that and use a soap designed especially for cleaning spray tanks like Nutra-Sol, then rinse once or twice to get the soap out.
Furthermore, you really should check your fittings, lines and nozzles to make sure it is all in working order before the new season is underway. Good to check your filters and check valves for the inevitable build up of gunk and crud. Depending on the materials you are spraying, some types of nozzles wear out after substantial use and are no longer delivering the amount of material they are rated for. Look to change those out as need be.