Rub auto paste wax on new resin furniture to keep off dust and dirt. When necessary, wash your furniture with a hose, rub down with soapy water and rinse. As an alternative, hose down, apply a paste of baking soda and water and rinse.
For dirtier furniture, rub on a mixture of water, bleach and detergent (about a gallon of warm water, a cup of bleach and a few good squeezes of dishwashing soap). Let sit at least 10 minutes, and rinse off. Reapply as necessary. For scuff marks, rub on a paste of water and powdered cleanser such as Ajax. Let it sit, then rinse well.
If you want an environmentally sound solution for removing stains, try a gentle product such as Simple Wash (see Resources below). Just as you would with bleach or cleanser, apply this with a sponge or cloth, let it sit and rinse off.