What is the best way to put a decal on a car?

Each decal has it's own set of instructions. But if want to be able to take it off later, I suggest placing the decal on the gl on your car, that way if you get sick of it, you can go to your local hardware store and buy a decal remover for two or three bucks which is a very sharp blade designed to scape off decals without leaving any residue.