Treat your wood furniture with a preservative, available at most home supply stores. Furniture made from cedar, redwood, oak and pine needs a preservative to prevent decay and rot. Preservatives are water-based or oil-based, but only water-based products are approved for extended contact with people. Because penetration is different for different types of woods, make sure the preservative you choose will work well with your specific grain. Apply the preservative with a paintbrush in a well-ventilated area.
Apply a coat of polyurethane after the preservative has dried. The polyurethane will add a protective layer over the preservative, improving its water resistance and durability. The polyurethane you select will depend on the wood grain and your color preference. Apply one coat at a time, adding another coat if you want a deeper color or if the manufacturer's instructions call for it.
Clean the wood furniture at least once a year. Add 1 tbsp. of bleach and 5 tbsp. of dishwashing liquid to 1 gal. of water and gently wash the furniture with a sponge or soft bristle brush. Rinse the furniture and let it dry completely outside.
Touch up spots that have experienced wear and tear with polyurethane or stain. Covering the furniture with a waterproof tarp is also recommended, especially during the winter.