Rodent-free building that's solid enough not to fall on the car in a heavy snow or storm. A good car cover is recommended, but will do nothing for keeping the underside dry -- a dry cement floor would be ideal.

Tires off the ground. Parking brake off.

Drain gas tank if the car can be stored in a low-humidity environment where condensation will be minimal. Otherwise, fill tank most of the way and add some Stabil. The remaining space is for a gallon of racing fuel when the car is revived.

Fresh oil in the crankcase. Remove spark plugs and squirt a good dollop of gear oil in those holes -- lighter oil will just seep down to the crankcase in short order, and you want to keep the rings from sticking to the cylinders. All this oil gets changed again before running the car at some future date; this is strictly for storage. Replace plugs -- note that there are dessicant holders that go in the place of the plugs for storage, but I haven't tried them.

Loosen all valve adjusters fully.

Make sure cooling system is full with a proper blend of water and anti-freeze that has anti-corrosive properties. A full system corrodes less than an empty system.