If you want to keep a good-looking deck, you have to treat it like the floors inside your house and give it a regular cleaning. Typically, this means sweeping it a few times a week to keep it free of debris. When you see bird droppings or food stains, give those a good scrub as soon as you can. If you keep potted plants on your deck, try to keep them elevated to prevent staining of the deck underneath. All of these tasks will help keep dirt from building up, which harbors living organisms that create slick surfaces. A yearly power wash isn't a bad investment either.