Before you start, make sure the workspace is up to the job. Dry and low on dust are the two requirements. Give the car a thorough wash first so that no dust or grit gets in and spoils the finish.
Next, clean the glass you are about to tint so the surface is genuinely clean, paying particular attention to the top edges. Once cleaning is done, dry it thoroughly.
Now for cutting the film. Trim it to match the size of the window. Spray a little water on the glass, hold a piece of plastic sheeting against the window and trace a template around the edges, leaving a little extra all round.
Front and rear windscreens also need heat-shrinking to shape. Lay the cut film over the outside of the glass and shrink it with a heat gun. This step is critical, because both the temperature and the technique matter: done badly it will blacken the film or crack the glass.
While shrinking, set the heat gun to high temperature and high airflow, then sweep it back and forth the way you would dry your hair. Never hold it in one place.
Once shrinking is done, start the installation proper. 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 place. Mist a little water or solution over the film as you work and use a triangular plastic squeegee to push the water out; a bank card or loyalty card will do if you do not have one.