Lots of opinions.
If you are going to be three years I would say just leave it on its tires and plan on buying new ones when you get back.
If you have new tires on it I would sell them and put junk ones on it.
I would also definitly change the oil before putting it away.
I also reccomened coating the engine and suspension parts in a light coat of oil.
It is easier to clean up oil than it is to remove oxidation.

I'm sure more people will chime in with more ideas.