Scrape off the surface rust with a wire brush. Scrub down to the bare metal. Home improvement centers sell wire brushes.
Put on rubber gloves as protection. Make certain you have plenty of ventilation if you are cleaning the furniture indoors such as in a basement or garage.
Apply a commercial rust remover with a steel wool pad. Leave the remover on the rusted areas of the furniture for around 10 minutes or however long the label instructs you to leave it on.
Scrub the rusted areas of the furniture with a steel wool pad. Rust removers are very good at dissolving rust because of their strong acids.
Apply a rust-inhibiting primer to the formerly rusted areas with a paint brush. Be certain that the primer is suitable for metal. Let dry. Apply a second coat to the metal furniture if the label suggests that you do. The primer will stop further rust formation on your metal lawn furniture.