Here is what i do when a car will be sitting (this would be longer than that time period though)
Full tank of gas-This applies more to older cars, prevents rusting. Use fuel stablizer though as the gas will loose octane over time.
Put it on you old stock wheels/tires if they aren't important to you. Easier than keeping a car on jack stands.
Disconnect battery, or buy something that trickle charges it.
Change oil when you start driving again.
That's about it, for 3 months, it's not as critical, this is what i would do when i stored a car for up to a year without driving it when i moved to central cali.