Decorating in authentic, New England nautical style is not intuitive. It takes restraint, and an eye for traditional furnishings. The style that I am describing is not "beachy" or "coastal". I am discussing the traditional New England design found in houses in old towns by the ocean. "Preppy" isn't a synonym for this design style, although east coast nautical style is definitely one variation of a preppy design style. The following concepts characterize New England nautical style.
Traditional furnishings: Think antiques imported from "East India" in the 1800's. Don't go crazy with decking your house out like The House of Seven Gables; a little bit of scrimshaw goes a long way.
Classic wood furniture: Southern beachy style lends itself to painted furniture, while the classic New England nautical style is characterized by simply finished or refinished classic wood furniture. That's not to say that you won't ever find painted wood furniture in a New England nautical style home. It's more that classic wood furniture has that Colonial look that is so very nautical and New England.
Dark front door with contrasting light trim: Colonial houses in seaside New England towns often sport front doors that are painted a dark color, with trim that is painted white or cream. Traditional brass welcome signs are also de rigueur, such as "golden cod" or "golden pineapple" plaques or door knockers.
If you decorate with sailboats, go big: Molly Frey is an interior designer based in the very New England and very nautical town of Marblehead, Massachusetts. If you scroll through her portfolio (the way her site is set up, I can't link to the single photo that I want you to see), you'll see a huge model sailboat set against an off-white wall. It's an excellent example of decorating with model sailboats. One little sailboat does not New England nautical style make. You need many model sailboats, or one very large one, to say, "Hey. This is New England, and we are sailors."