General advice:
1. Get a passport. You can technically go on some cruises without it, but it's more work and would be a pain if you had to fly home from the cruise early.
2. Generally the advice is to book as early as possible, but I'm assuming you're not booking through the normal public method.
3. Cabins right below the pool deck or close to the engine can be noisy, so avoid those if you're a light sleeper.
4. If you get sick on any rides, cars, planes, or any other form of motion, bring some Dramamine or look at getting Sea bands.
5. Try to get a reservation for Palo brunch if you can, it's worth the extra cost.
6. Make plans for your port days, don't just get off and walk around. You'll have plenty of time to rest on the sea days. The one exception is
Castaway Cay. There, you can just walk off, grab a chair, and enjoy the beach for the day.