Sand down any splintered, rough or scratched areas of the deck with 80-grit sandpaper, then sweep the deck carefully, cleaning all dust and debris off of it. Make sure to get the areas between the boards as well.
Wash the deck down with a pressure washer. This blasts off most debris and dirt and preps the surface nicely. Set the power washer to 3,000 psi. If you use any more pressure, you could do damage to your deck. Also, the only end you should use is a 40-degree fan tip. Let the deck dry for several days.
Strip the old stain off your deck, using a deck stripper. Make sure to use a product designed to work with the type of wood your deck is made from, as not all products work with all woods. Wear protective gloves, eyewear and overalls, and strip the deck according to the directions on the product. Rinse the deck thoroughly and ensure it is dry before moving on.
Apply a wood brightener to your deck. Wait the amount of time indicated on the product, then rinse it off with a garden hose.
Spread an even layer of stain over the deck after it has dried. Pour the stain into a paint tray and use a roller with a handle to do the main portions of the deck. Use a paintbrush to get into the tighter creases or corners. Allow the stain to dry completely before using the deck.