I have a car that's been sitting for several months and I just got it working again. What should I do to ensure that it keeps running well?
Replace all the fluids (don't forget the transmission and rear diff!) and the battery and check all the hoses for cracks. Drain the gas tank en fill it up with new fuel. Check the tires, they will be in bad shape and might need replacement. And of course drive with it, that's what cars are meant for. :)
Drive it at least once a week for an hour and maintain it per the owner's manual.