It's Time to Clean
This is the step where you get to take years of gray color, dirt and more off the deck. Applying the new deck stain to a clean surface helps ensure good penetration and adhesion so you don't have premature peeling and wear. And the finished deck will look much better.
First, if you have flowerbeds or landscaping right next to your deck, water thoroughly, then cover with the plastic drop cloths. If you do this, the deck cleaner won't affect the plants.
Clear the deck of all furniture and get ready to start!