Look for dark areas of wood oxidation and tannin bleed, these can be removed with a wood cleaner, followed by a wood brightener. Follow the wood cleaner instructions and apply with a power applicator, or you can use a pump up garden sprayer. Some may choose to sand the deck as well, focusing on splintering and handrails.
Let the solution set for 15-20 mins and simply hose off. DO NOT EXCEED 1000 PSI when using a pressure washer or the wood may get damaged. Keep cleaning solutions wet by misting with water. Allow surfaces to dry thoroughly for 24 hours before applying the stain.
Using a brush, roller or sprayer, apply the stain at a rate the wood can absorb. Work the stain into wood by back brushing (see video for example). Your wood will be ready for foot-traffic the next day and will remain beautifully preserved for years to come.