If it has transfer paper on it you don't want to get it wet. It will make it very difficult to remove. Tape it at the top and then fold it back over, apply the water to the car, pull the backing paper off and squeegy from the top down. If you start at the middle when it's still taped to the car with the backing paper still attached your asking for wrinkles or an alignment issue.

For aar type stripes you can tape the whole thing to the car and then cut between the stripes and do it in sections to make it more managable.