Cleaning a one year old deck before treatment

I just bought a cottage along the coast of Maine. The deck was built last year of treated Southern pine and nothing has been done to it yet. The deck is mostly in the shade with a few hours of sun. Doesn't dry out much during the summer and the winters are pretty hard. My question is what should I use to clean it properly? Then I will go to the Deck Treatment forum and ask what is the best deck treatment after cleaning. Thank you!