First dust each item, then wash it in a solution of mild detergent and water. Check all nuts, bolts and screws and tighten any that are loose. Missing, broken or rusted fasteners should be replaced with rustproof ones made of aluminum, galvanized steel or stainless steel. Next, lubricate all hinges and wheels with a silicone lubricant. Oil should be avoided because it tends to cake and attract dirt.
Additional care depends upon the material the furniture is made from.
Aluminum furniture resists rust but has to be safeguarded against any type of pitting that gives the metal a dull patina. Frequent washings help prevent this condition if the metal is in good shape or has an enameled or baked-on finish. If the metal is already in poor condition, more than washing will be needed to revive it. If the aluminum furniture is in poor condition, rub each piece briskly with a steel wood pad. Once the metal is smooth again, wash it in a mild detergent and water solution.