Couple of things come to mind...
1. Try to schedule your arrival to the ship early so you can board without having to stand in a massive line. Most people for the 7 day I went on showed up later in the departure line.
2. Plan on not seeing your luggage for awhile when you arrive. We, the ex & I, arrived dressed as if we walked off the airplane. While waiting for the ship to leave, I wanted to change but all our clothes were packed away. We did have access to our room, but that was it. I don't think the luggage showed up until late that evening. My advice, pack your toiletries and a change of clothes into a backpack or a small carry on. I'm unsure of the rules, but since your luggage must go through customs -- no exceptions, you are allowed to carry on something.
3. Plan on spending more money than you already have. Everything on the ship, except for food, will cost you extra.
4. Don't pack your schedule full of excursions. Plan on taking some time to relax. Unless you like to be constantly on the run, planning for alot of excursions will have you worn out. Space them out and try to relax a little.
5. Get a room on or one floor away from the main dinning hall. You can be cheap and stay on the bottom, but you'll regret it unless you like stairs. The reason why is you should plan on being in the dining hall 3 times a day for food. Now you'll eat at other places from time to time, but the bulk of your eating is done there. If you've been in the pool all day, you'll have to go all the way to your room (down stairs), change, then go back up stairs. Doesn't sound like a big deal, but the place will be packed and time will be wasted getting from place to place. Forget about the elevator unless you really need it. They will always be full during peak movement times.
6. Decorate your luggage. When you leave the ship all the luggage will be dropped into one large room. Everyone has black luggage that looks like yours. If your plane leaves early, you'll have to look through rows upon rows of luggage to find yours. I have green luggage that I tied ribbons to. I saw it walking off the ship and was able to grab it within minutes. Most people spent a long time looking for it. Picture a warehouse full of luggage and then you'll undertand why this is important.