I'm going to Hawaii in late December, right when the salmon runs start dying off and I turn my attention to Steelhead. Booked a guide and everything, can't wait to throw some flies at Bonefish and Tervally on the flats.
If you have a day or so and you're on Oahu, try to see if you can book a day with Chris of Hawaiibassfishing.com and fish Lake Wilson up in Wahiawa. Lots of fun fishing for Peacock bass and if you're lucky, get the Lake Wilson slam (Largemouth, Small mouth, and a peacock!). Throw in some purple cap-spider flies for the Red Devils as well!
Hey man, based on the time of year you're going at (December), I would focus more on the inshore fishery (barracuda, bones, and papio/omilu) than the deep. During the winter months the off shore fly fishing can be pretty shitty with the seas being brutal. It might not look like it is from the beach, but beyond the reef edge and the breaks the water is pretty brutal- not something I would want to be standing on a deck casting in. That being said, you can't catch fish if you're fly isn't in the water. Except the water at that time of the year can be pretty rough. There's a reason they hold the Eddie during that time of the year *wink.
You might have better luck off Kona during December, but on Oahu it might be tough.
Also, Hawai'i is not your Maldives or anywhere else that has white sandy bottoms with unobstructed beach access so running the beaches tossing flies at bones is going to be hard. There is a mix of seaweed, rocks, coral and sand. The bonefish come up onto the flats, and then go off the flats- they don't live on the flats like other bonefish locales. You're best bet is to hire a good guide that has access to a flats skiff so you can shoot to different areas of the island during the different phases of the tide. I know Terry has a new 16 foot Shipoke Abaco that drafts 6''. Maybe give him a call or email and book with him if you haven't gotten a guide yet.
If a guide is out of reach, then a lot of the public beach parks east of Diamond Head offer some decent (during the winter, at least) channels to mostly blind-cast into, and if you can spot fish, there are times of the day when you can sight fish them. But hey, do lots of homework, tie lots of flies (you'll defs lose some to the coral), and practice casting (20mph winds are regular) and you might just feel that tug we all call the drug.