So, you think you're ready to to brave the fog and find Kasumi Nakano, eh? Well, we've got a couple of pointers that should help you on your journey. Image credit: Serum
FIRST OFF... this may seem obvious, especially given the trailer for Far Harbor, but! You absolutely must bring Nick Valentine with you. Some of the biggest payoffs/quests in Far Harbor's story revolve around Nick, but for whatever reason, the game does let you play the DLC without him.
Have you lost Nick somewhere? Good news, at least if you're on PC. There is a mod that will help you track down your companion, no matter what random-arse radioactive ditch you left them in.
At one point, Far Harbor actually offers you a permanent new companion, Old Longfellow. And while Old Longfellow has some great lines, I still wouldn't trade him with Nick. Not for the DLC, anyway. If nothing else, make sure to have Nick with you when you enter/explore Acadia!
Second, you should bring whatever rad resistant gear you have with you. Power Armour works, the Hazmat suit works. Maybe you've got something else with rad resistance, whatever it is, take it with you — including chems, such as RadX and RadAway. The island of Far Harbor is inundated with radiation thanks to the fog, and that stuff adds up. Think of it as the extra New England version of The Glowing Sea, crabs and all.
Finally, prepare for actual skill checks. I know — I was shocked, but the game does give you lots of options depending on your character's build. It might be worth bringing along some light gear that influences SPECIAL, in particular charisma, because that's actually useful now.
Oh, and yeah. You should totally buy that Harpoon gun (if not Old Reliable) at the first vendor in the DLC. They're both pretty cool.