Power Wash or Sweep
Getting started, remove the Grill, furniture and etc off the deck. Then power wash or sweep it to remove leaves and dirt. Use something thin like a putty knife to remove any debris stuck down in the spaces between the boards.
Using a Cleaner
Now use a standard deck cleaner to remove stains. Make sure to follow the directions as some cleaners require the deck to be wet before applying. Use a stiff-bristled brush broom to apply the cleaner. Once the entire deck is cleaned, let it soak for a period of time. Make sure you follow the directions of the cleaner.
Once it has set for recommended time rinse thoroughly. Allow the deck to dry for at lease 48 hours.