You should know that each one of the bigger islands, Oahu, Maui, Kauai and the Big Island are all different, really different.
They all have a different vibe, different landscape, different beaches and before you go that far you should either talk to someone that can recommend the best island for you or do your homework. The Big Island has 11 different climate zones! If you're planning on driving out to the volcanoes, bring a coat, think 35 degrees! Flip flops and a tank top don't work up there. But who knew?
It's important to plan ahead. A rental car will cost less if you prebook than if you just arrange one when you get there. Some of the more popular luaus will fill up and even Pearl Harbor should be reserved on line before you go to avoid wasting precious time in paradise.
And you know the line, location, location, location? Even 5 star resorts are not all alike. Where they are located on the island makes a difference. Princeville on Kauai gets a lot more rain than Poipu on the south end of the island. WaIlea and Kaanapali are both on the same side of the island on Maui but are very different. Kaanapali's beaches are always rated among the most beautiful in the world.
If you're going that far consider seeing more than 1 island. Once you get there, they're not that far apart. That's why I'm a fan of the NCL 7 day cruise around the islands. But if you've dreamed of watching the sun go down sitting on a beach and sipping a Mai Tai, then choose an island and spend some time there.
If Hawaii is on your bucket list and the numbers say it is, then plan ahead to get the Hawaii experience you've dreamed of. It's really worth your time.