Peel the paper protection from one side of the Plexiglas. It usually has protective paper adhered to both sides because it scratches easily.
Use the spray bottle and squeegee the Plexiglas clean. Dust adheres to it quickly.
Spray a thin layer of soapy water on the Plexiglas.
Spray a bit of water on the film and start peeling the backing off. Spray a bit more water on the film as you remove the backing to help keep dust from clinging to it.
Remove the backing and carefully set it in place on the Plexiglas.
Squeegee the soapy water from under the film, starting in one corner and working over the entire piece of Plexiglas.