I have never heard of diesel fuel going bad from sitting over a winter. The one thing that I would do to the fuel system is drain the water separator, if equipped, and/or install a new fuel filter. I have also been told to store things with a full tank of fuel, to prevent condensation and corrosion in the tank, if it is steel.
Changing the oil is a good idea, and I like Lucas oil treatment, as it helps prevent a dry start when you pull the machine from storage.
Also I would also make sure that you have no water in the bottoms of you hydraulic reservoir/chain cases/gearboxes, if you machine is so equipped. Grease everything, and store it with all hydraulic cylinders retracted, if possible.
My $0.02 - SR