The fall, while the weather is still mild, is the perfect time to prepare a wood deck against potential damage like checking and splitting that can occur during a wet, snowy winter. The first step is to apply a deck brightener to the surface to loosen ground-in dirt and stubborn grease stains. Then rinse the deck with a garden hose or, better yet, a power washer ($50 per day to rent).
Once the deck is dry, apply a clear wood preservative to bare wood or a decking stain to previously stained surfaces. If you're staining, choose one that contains a wood preservative. And don't forget to coat all end-grain surfaces, which tend to soak up water and crack if not properly sealed. Use a 2-inch-wide foam-rubber brush to coat the long edges of the deck boards, forcing the applicator down into the space between two boards and sliding it along to spread the finish.