Remove any leaves that are stuck to the chair first. Rain is common in the fall, and wet, dead leaves can easily become stuck to lawn chairs.
Wash the lawn chairs next. Take a bucket of soapy water and scrub the chairs as thoroughly as possible. This will clean off any leaf debris that remains on the chairs after the large pieces have been removed.
Use a Mr. Clean Magic Eraser to scrub any areas of the chair that are still stained. The Mr. Clean Magic Eraser works far better than a regular sponge because it penetrates into the grooves of the chair and can remove any dirt or stains that exist without harming the surface of the chair.
Use a bucket of equal amounts of bleach and water to further clean a white lawn chair if it has not responded to scrubbing with soap and water or to the magic eraser. Be sure to wear gloves to protect your skin and rinse the chair with clean water when you are finished.