Got this from Phil Bailey's blog several years ago.
Follow this procedure if you are storing a car for a few weeks or months
1. An oil change, unless the oil is high priced synthetic and comparatively new.
2. A good waxing and cleaning inside and out
3. Add fuel stabilizer to a half tank of gas. Run the engine until the stabilizer reaches the injectors, about one minute or so. Five minutes is more than enough. The half tank of gas will allow you to run down the road when you are putting the car back in service and top it up with high test until that whole tank of fuel is gone. Then go back to using regular fuel. If your car uses high test anyway, it's not a good idea to have too much fuel in the tank.
4. Inflate the tires to a safe but higher than normal pressure, 38 psi is good. Do not put the car on blocks. It exposes the shock absorber pistons to moisture and is not worth the trouble.
5. Disconnect the negative battery terminal and write a note to yourself in next year's calendar to charge the battery for about four hours on the first of each month.
Do NOT be tempted to start the engine frequently for a few minutes. This is a really bad practice.
When you put the car back in service pull the fuse for the fuel pump and crank the engine over until some slight amount of oil pressure starts to show on the gauge or the oil pressure light stays off. Put the fuse back in and the engine should fire.
Exceptions
1. Never disconnect the battery or allow it to run-flat on late model cars such as BMWs with I-Drive and Mercedes with the Command system, or any car with electronic controls such as a stability system. If you do, the car will have to be towed to the dealer for a full day of expensive reprogramming!
2. If you have a theft protected radio that goes into "fault" mode if the power is disconnected, make certain you have the restart code for your unit.
3. To avoid these dramas with computer programming use a 1-amp trickle charger connected permanently to the battery. If your storage area lacks electrical power you have no choice but to start the car every two weeks or so and let it run for about twenty minutes. Snow is not harmful to your car, but salt is. Let the car run in your driveway or somewhere else without salt slush.
4. Don't be tempted to store the car outside. Creeping dampness will permeate every part of the car and the brake rotors will be toast.