I don't think it's really necessary to pick an island as a first step. There are great things to see and do on each island, and I think most of us end up returning (time and time again) to see the other islands and return to our favorites. Airfare is about the same to any of the islands, so that's not a factor.
I would research the top resorts on all of the islands, pick a timeframe that you want to go, decide on the trip length (one week, two weeks, more?) and set up an ongoing search. Once you have one week booked (if you're doing more than one), set up ongoing searches for any additional weeks (probably expanding your resort selection since you're probably being more specific on dates now). Once all of the weeks are booked, book your airfare (or start watching for it, if the prices are too high now).
If you want to visit multiple islands, I would focus on Oahu and/or Maui for the first exchange. Kauai and the Big Island are much easier to get through RCI Weeks. It's easiest to get the hard exchange first and work around that.
That's just me, though. There are lots of ways to do it. I think this gives you the best chance of getting a top resort, though.
