Jack up the rear of the car, one side at a time if that's easier. Squeeze all the air out of the airbags and put the plastic cover over the air inlet to stop it from inflating back to full size. Put some soapy water on the outside of the airbag. Slip it into the coil spring, then take off the cover so it can suck in air and let it pop into place.
Common place to run the air lines is to behind the license plate with the gas cap. Fill them up carefully, it doesn't take long for them to reach a decent pressure, remember you aren't filling up a tire or you'll blow them up.
