Driven during winter:
Air up the tires. Check your spare too!!!
Change the oil and oil filter. In REALLY cold climates, consider a thinner oil.
Check/change the antifreeze. Make sure your heater valve is open so the coolant in there drains out too.
Apply Rain-X on your windshield. It works.
Change the wiper blades.
Apply dialectric grease every accessible connector and light bulb socket.
Wash and wax.
Load your winter survival kit: Rope, tow/recovery strap, ice scraper, tool kit, a knife, duct tape, bailing wire, a flashlight, a blanket, gloves, and an extra pair of socks (Wet socks suck). Two bottles of water, power or granola bars
In the spring, consider applying gloss black paint behind all body panels or other undercoating. Vehicles up to the late 70s had very light or no underbody protection. Another benefit is that it is easier to clean since gloss paint is smooth and less likely to hold dirt/mud like a rough surface.

Long-Term Interior Storage:
Air up the tires
Wash the truck thoroughly and blast the areas known for rust on these rigs:
1. Behind and above the rear wheel well liners that are welded in. Mine had packed mud and pebbles that clogged the drain holes. 'had to replace a wheel arch last year.
2. Behind the front fender liners (the tar paper stuff).
3. At the front fender, the area above the lower mounting bolt near the door.
4. The cowl and its drainage course. Remove the rubber plugs above and behind the front wheels. Take out the leaves, twigs, etc. Rinse thoroughly.
Give it a good wax job if your paint will take it.
Fill up the gas tank(s) and use a bottle of Sta-bil.
change the oil and oil filter. Oil turns acidic over time. Let it run for a few minutes.
Place the rig up on jackstands to unload the suspension. If on a dirt floor or other porous surface, first lay down a sheet of plastic and place jackstands on two layers of 3/4-inch plywood to spread the load and prevent the stands from sinking into the earth.
Take a can of WD-40 and spray the entire under carriage. It's a light oil and will easily wash off in the spring.
Remove the battery and store the battery in a cool dry place. Preferably connect it to a maintenance charger.
Remove the spark plugs and inject a tablespoon of oil into each cylinder. Rotate the engine by hand a few times to lube the cylinders. It'll smoke a bit when you bring it back to life in the spring but that's okay. Your cylinder walls will thank you.
Vacuum the interior and remove all trash.
Place fabric softener sheets in the interior. It'll stave off musty smells.
Close the fresh air vents to prevent critters from getting in.
Crack the driver and passenger windows like 1/4-inch so the interior can breath.
Plug/wrap/tape closed the exhaust tips so critters don't go crawling up the tail pipes.
Option: Install some mouse traps in the engine compartment that are baited with peanut butter. Do not put any in the cab cuz it'll just be an invitation for them to come in.

Never use Armor All or any other protectant unless you are dedicated to using it regularly. My 65 'Stang was regularly doused with that crap and the hot California sun has outgassed the vinyl and the protectant and constantly leaves a nasty film on all the windows. The vinyl is now dried and cracked too. Stupid stuff IMO.