Mask the surrounding area by covering any exposed paintwork, mouldings, glass or bumpers within a minimum of two feet if using aerosols. If using professional type sprayguns a much larger area will need to be protected. Start the masking from an inch or so beyond the sanded area. If primer is applied to unsanded paintwork it will be impossible to "feather-edge" the repair due to poor adhesion of the primer to the unprepared surface. When joining additional sheets of paper to each other, use masking tape along the full length of the join, otherwise a surprising amount of overspray can collect on the panel beneath the paper.
Likewise, a much tidier finished repair is obtained by masking wheel arch openings to protect inner arches, plastic liners and mechanical parts from accidental overspray. Finally, don't forget to cover wheels and tyres if needed, either with normal masking methods or proprietary wheel-masking covers.
