If you have metal patio furniture or even metal chairs in your house, you can repaint them easily to make them look like new. But be forewarmed, you will need to strip the old paint first, or else the chair will only look marginally better. Be sure to work in a well ventilated area or work outside on a nice day.
First, use paint stripper and apply to the metal with a clean brush, applying the stripper in one direction (not brushing back and forth). Follow the instructions on the paint stripper for how long the product needs to sit on the metal. Remove any bumps and bubbles with a paint scraper.
Next, wash the chair using mild dishwashing soap and water. Rinse.
Using steel wool (available in hardware stores, too) you will need to scrape away any leftover paint, paying close attention to crevices and joins in the metal.
Next, use a paint primer on the chair, one especially made to prevent rust. This will help prevent your chair from getting rusty when used outdoors. Allow to dry following the directions.
Now paint with your regular paint, again designed for metal and for use outdoors (usually called exterior paint). Allow to dry and apply second coat as needed.
If you are unsure which primer and top coat to use, consult the paint department of your local hardware store when you purchase the paint.