Hawaiian Vacation Advice: I don't know what to do there.?

I am going to suggest a book called "Hawaii for Dummies" by Frommer's publishing. It breaks down all the islands, what to see on each island, where to stay, where to eat and different activities by type (sightseeing, hiking, snorkeling, history, shopping) so you can pick and choose activities that suit you. It will prioritize different things to do if you are there for a few days or a week or longer.