Spread out a series of drop clothes around the metal gate to protect any vegetation surrounding the gate and ground.
Scrape any rust off of the gate using a stiff-bristled wire brush.
Smooth the rust spots using a 120-grit sandpaper.
Thoroughly wipe down the gate using a rag to clear away any remaining dirt and debris.
Apply an exterior metal primer onto the spots sanded down and affected by the rust. For rust spots that are heavily pitted, apply the primer with a paintbrush to ensure that the entire surface receives a solid coating. For the remaining spots, use a primer available in spray can format. Using a spray can is easier and also reduces brush strokes on the gate.
Allow the primer to completely dry for 6 to 8 hours, then spray on the finishing coat of enamel paint. Be sure to find a metal paint that is compatible with your choice of primer. Allow the gate to dry completely for 24 hours, then remove the drop cloths.