I lived on O'ahu for four years, and I second most of what Alan said. I've quoted below the things I wanted to highlight.
Be prepared for a completely different world. I would emphasize how difficult it is for a mainlander to be truly accepted by local culture. Alan's right, as a black guy you will often be treated better than white folks. Locals are mostly either native Hawai'ian, or the descendants of Japanese/Chinese/Filipino/Portuguese immigrants who worked the plantations. The haoles (white folks) were the overseers. Turn about is forever fair play, and you will get credit for being oppressed on the mainland. You get credit for ANYTHING other than being a straight white guy, so being gay generally was helpful, too. The anti-white mentality sucked for me, but for you, enjoy! Be prepared to be weirded out when some big Tongan dude affects his perception of a black accent and calls you "My brotha!" It will happen.
Local decisionmaking is highly influenced by Japanese culture (people say "Asian," but that aspect is really Japanese). You have to come to consensus in a long, roundabout way, where no one says what they really want or think. It can be frustruating until you get used to it. If you are too loud or too forward, you're just a pushy mainlander and you will be ignored.
People will say extraordinarily rude things, like "Where are you from, and when are you going back?" Learn to let it flow over you or you'll waste a lot of time in fruitless anger.
The one place I'd disagree with Alan is about pidgin. Don't go overboard, but my experience is that if you let yourself gently be influenced by the local accent over a period of time, and learn to throw in some Hawai'ian words and local slang, it's viewed as RESPECTFUL, and a positive, not like you're making fun of people. My bf couldn't do it and he was sometimes a bit jealous of the extra crumbs of respect I got for it.
I also agree about joining business organizations. It will take a while, but if you persevere people will ulimately peg you as one ok moke, even though you're from the mainland. The flip side is, locals often have this inflated idea of the sophistication and intelligence of the dreaded arrogant mainlander. By the time you're semi-accepted, you lose this edge. Catch 22.
Spend time doing things you really enjoy and revel in them. For example, we had an outdoor shower, and I didn't shower inside the house for two years and oddly enough it's the thing I miss most.
-Be prepared to be "bucketed" in regards to social class. Acknowledge that you're immediately in the "Oh, you're not from here" bucket (malahini). Know that there is an unwritten but real "racist pecking order" which exists in social AND business circles. The more you study, learn, and apply local culture and customs the better the chance that the island will "accept you" rather than "reject you". The acceptance/rejection can be subtle but very real. Right or wrong that's just the way it is. "Tourists" get all the "Aloha" and red carpet treatment. Once you live there, now you're part of the ecosystem and you're competing for the same rice bowl. If you're in the military, it can be an advantage/disadvantage depending on how you leverage it.
-Be prepared for experience "American Guilt". You'll understand after you've read the books. Being a person of color, you will experience less of the subtle and overt prejudice discrimination than Caucasians. Yes, in some ways you will be "higher" on the social "totem pole" than white folks. Racism is an integral part of the culture. There is both open non-PC humor and more subtle racism at worst. Accept that this is part of the ecosystem. Navigate with knowledge from the books.
-When asked your opinion on anything social/political, it is best to respond with something like, "I'm not from here and haven't been here long enough to have an opinion yet. Can you tell me your thoughts on the topic?" Then shut up and listen. Avoid coming out on one side or another on an issue as you will "lose" with somebody. Avoid criticizing anything "local".
-If you're not into hiking, learn quick. It's one of the most valuable opportunities to enjoy nature that you may encounter in your life. Heck, NorCal has great hiking but not as good as Oahu.
-Be prepared for everything to run slower. Be prepared to be patient. Businesses, social gatherings, government. Everything. Go with the flow or you'll drive yourself nucking futs. Traffic is a good example. Speed limits around town are 25mph. Yes, 25mph. And, people generally don't speed (because there are oodles of cops who WILL stop you, ticket you, and take 45 minutes to do it), nor is "horn blowing" legally permitted unless it is an imminent emergency. You can get a ticket for blowing your horn.
-People are nosy. Expect everybody to want to "get into your business, personal life, etc." Watch what you say...even standing in line at Foodland. You just never know who is listening (and everybody is listening) who is so-and-so's cousin's auntie's son-in-law's sistah or brah.
-Don't try to speak pidgeon. If you weren't raised with it you'll come across as an ass. You can "pepper" your conversation with a word or phrase when you learn and know when it's appropriate, but don't try too hard. It will make the locals' eyes roll.
-For business, make sure you join multiple professional associations. It's one of the easiest ways to make inroads into what is in reality a very closed ecosystem. Don't expect business to accept you with open arms. It is all about making and cultivating relationships BEFORE folks will do business with you.