Rust
Removing rust stains on Fabric, cloth furniture and carpet: Squeeze enough juice from a fresh lemon to thoroughly saturate the spot. Generously sprinkle on some salt. Refreshen the lemon juice every 2 hours during the day then let it set overnight. Rinse with cool water and repeat if needed.
Metal surfaces: Treat metal immediately. It's easier to treat a small spot than to sand and repaint. Use navel jelly from an automotive supply store.
Removing rust from wood generally requires sanding and refinishing the wood. Try dabbing on a bit of lemon juice on the spot. Wait 10 minutes then blot and repeat. If that does not help then the furniture must be sanded.
Always protect surfaces when setting anything metal down. Metal tends to sweat causing the rust.