@sullyfish6,
It depends on the car and where it will be sitting, but if it is not something special, I would disconnect the battery (so it wont drain), make sure the gas is completely full so it wont go bad, and make sure it has decent antifreeze (which it almost definitely does). For only 6 months, it does not need to go off its tires, but it should be checked up on. Keep the tires inflated, and if possible, start it up and move it once every month or two. If it were more long term, you would put it on jacks and change out all the fluids. If it is outside, a decent car cover that straps on should do the trick. One other thing to watch out for whenever a car sits is mice and other animals making a home in it. For this reason, it doesn't hurt to just open up the hood every one in a while and looks for evidence of this