How to prepare a car for storage?

Gas it up, an empty tank can rust. I would keep all the old fluids in there, and change them after the first 30 minute start up of spring. They will collect all the moisture and crud that grew in there over the winter and will carry them out with your fluid change. They have these huge $150 bags now that you can drive your car into and ziplock close, pretty cool! if sealed, Throw an open bag of rice in there too to absorb any moisture.