I'd start with:
Remove the avionics. Place them in baggies with desiccant. Store in a safe, dry place.
Dump the oil. Refill with all the automotive oil you can get in the engine. Might take 20 quarts, who knows. It'll probably leak, so put a pan under it.
Squirt one of the thick(er) LPS sprays in each cylinder. Maybe LPS3.
Drain the fuel system. Tanks, lines, pumps, carb bowl, gascolator, everything.
Drain the brake system. Fill with new non-hygroscopic fluid.
Remove the battery.
Spray every hinge, ball joint, heim joint, etc. with LPS 2 or LPS 3. In fact, spray down all unpainted steel surfaces with one of those.
Remove the interior. Bag it, store it with desiccant in the bags. You don't want critters finding a nesting place.
Cover the airframe with old sheets, a parachute, etc. Put mouse/rat excluding devices on/around all wheels. Put bars of critter poison around the perimeter of the hangar.
Have someone check on it regularly.
Alternately, find a partner who will fly it and keep it maintained while you're gone and skip all of the mothballing steps.