Start by choosing a dry, dust-free workspace. Keeping dust out is absolutely critical to the finish. Then wash the car and protect the surrounding areas. Liquid gets sprayed onto the glass during installation, so shield anything nearby that could be damaged. Use covers, towels or cling film.
Before applying anything, clean the window glass thoroughly, paying attention to the top and the edges that rarely get cleaned. Then dry it and make sure the surface is spotless.
Film is sold in large rolls, so you need to cut a piece to size. Spray a little water on the glass, hold the plastic film against the window and trace a template around the edges, leaving 3-5 mm of margin all round.
Windscreen and rear screen are both curved, so the film has to be heat-shrunk to shape first. Lay the cut film over the outside of the glass, set the heat gun to its highest temperature and fastest airflow, and heat the curved areas quickly while pressing the film onto the glass with a scraper. Do not hold the heat gun in one spot for too long or you will damage the film or crack the glass.
Once the film is shaped, you can start the actual installation. Spray water or window film solution onto the inside of the glass, peel off the innermost plastic liner, apply the film to the inner surface and slide it into position.
Finally, mist a little water or installation solution over the film and use a triangular plastic squeegee to push the water out; a stiff card works if you do not have the proper tool. When you are done, check for bubbles, adhesion, creases and scratches. If all is well, blot the water from the edges of the glass with a towel.