I'm a newbie however this will be my 7th cruise since May 2006 so here are my "don't leave home without them":
1. An over the door shoe rack. With girls sharing cabins, this has kept our cabin incredibly organized.
2. From Target: They have a travel clothesline - this proved invaluable with three of us on Liberty in one cabin last spring - swimsuits, workout wear etc. Buy some extra clips. You might even find a use for this at home.
3. Don't forget your chargers for your phone, camera, etc. camera charger, transfer cords, etc. I believe you can use the cords to transfer your pictures to have them put a disc while on the ship.
4. Notify your credit card companies that you're going outside the US and your bank too.
5. I just heard this one from a coworker cruising the same time I am: use a large multi compartment pill box for your earrings, etc.
6. Don't forget there is drawer space under almost all of the couches/sofa beds in the cabin but don't forget to check there when you leave.
7. Put your name and address on everything and your cabin #! Camera, camera case, etc.
8. Don't forget to have a good time, don't worry what everyone else is doing. Take time for yourself if necessary.
9. An address list for postcards if you're the postcard type!
10. I don't know if you use dramamine etc. but I love the pulsing seasick watch type thing that you can get from drugstore.com.
11, Ziplock bags -- get a sandwich the night before if you know you're going to be on an excursion that makes you very hungry such as three reef snorkeling, etc.