Once your deck is finished and is starting to be exposed to the elements, there are several things you should be on the look out to ensure the wood continues to be properly protected. It's always a good idea to check for protruding nails and loose boards regularly. Over time you may see sap that has crystallized, commonly around knots in the wood--it can easily be removed by scraping or with a little turpentine. Try to keep the deck swept clear of leaves, which when they get wet could potential stain the deck surface. Before winter, remove items like potted plants and metal patio furniture to help prevent staining.