Place the chair on a drop cloth.
Sand the chair if it's made of wood or wicker or if it's a metal chair with rust spots. Remove any loose pieces of paint while sanding. Clean off all of the dust and dirt with a damp cloth and allow it to dry.
Shake a fan of spray-on primer for about a minute. Hold the can 1 foot away from the surface and spray the primer evenly on the entire chair. Allow the primer to dry for an hour, or as directed by the manufacturer.
Apply spray paint the same way you applied the primer, making sure the paint is well-shaken the whole time. Let it dry for several minutes, then apply another coat. Repeat until the desired color is achieved.