Dry the plastic lawn furniture piece -- such as a lawn chair -- completely.
Using the sandpaper, lightly sand an arm of the chair down so that its color begins to fade. Repeat sanding at least once more on the arm of the chair.
Spray an even coat of the chrome spraypaint from a distance of at least 12 inches onto the arm. If the results are satisfactory, continue to sand the rest of the chair.
Spray an even coat of paint onto the rest of the chair. If expense is not an issue and the chair will be used again, consider applying a coat or two of clear coat over top of the chrome layer.