Buy an over-the-door shoe holder to place on your bathroom door to hold all your toiletries, makeup, suntan lotion, etc.
Bring a power strip on the ship with you because there aren't many plugs in the room.
Bring air freshener to help diffuse the bathroom stinch that can be smelled on occassion.
If you have children, decorate your door so they know which one is yours . . . all the rooms look alike.
Unpack half the clothes you're going to attempt to put in your suitcase . . . you won't need all of that stuff!
Go to the disboard meet at 2:30 on the Promenade Lounge because it makes going to everything else on the ship more fun. You'll have many new friends to sit with in shows, wine tastings, in the pool areas, etc.
Those are the biggies!