Sweep up any dirt, leaves or other loose debris. Once the deck is clear of debris, scrub the entire surface of the deck with a commercial deck cleaner designed for composite decks.
Rinse the deck thoroughly with a garden hose. Allow the deck to dry completely before continuing.
Mix the composite deck stain thoroughly with a paint stirrer. The stain should be uniform in color. Pour the stain into a paint tray or small bucket.
Spread the composite deck stain with a roller or paintbrush. Work in sections so you will be able to walk around the deck -- start at the point that is furthest from the door or steps then work your way back.
Allow the composite deck stain to soak in for about 30 minutes. This wait time may vary by product so check the label. Inspect the section you stained for pools of stain -- roll or brush these areas out so that there are no more pools.
Wait for the stain to dry completely. Repeat the process until the entire deck has been stained.