Getting into shape?

Hey everyone, I just signed up and am new to swimming in a pool (and taking it seriously)! I'm from San Diego and I've surfed all my life, so I love the water, but now I'm living in New York City. There's no surf, and I'm getting fat! I've never really had to work out, except surfing, and I was wondering if there is something I should be doing other than swimming. Could someone maybe give me a few tips for training so I can get into shape before this summer! (my friends and I are going on a month long Caribbean surf trip)! I would really appreciate the help! Thanks -Joe.