Run it dry.
Change the oil.
Sharpen the blades (my Snapper has a Ninja Blade)
Spray a few squirts of WD-40 into the spark plug hole, replace the plug with a new one
Clean or replace the carb air filter
Wash it to get it clean, and make sure all grass and thatch is cleaned out from under the deck
Oil/grease wheels
By doing all this, the mower is SET TO GO next Spring by simply adding gas and starting it. No muss, no fuss.
Luckily, this year, my float stuck and I got a tiny bit of gas into my crankcase from carb unrestricted flow on the last mowing. This really cleaned out the crankcase - by accident. So I put in new oil, ran it for 10 minutes till dry stall, then changed the oil again to make sure all gas was out of the oil.