Number One - Your luggage may be several hours behind you to your cabin, pack a swim suit in your "carry on" so you can begin enjoying the ship facilities before your luggage arrives in your stateroom.
Number Two - The sun is bright, for those of us (mid 40s) only beginning to experience reading glasses, its tough out by the pool. Bring a book on tape or CD.
Number Three - Smuggle (in a lawful way) your own cokes/drinks on board. The cruise line rapes you on the price of beverages. I would love to find an "all inclusive" cruise line. This was the single biggest gripe I had and the single biggest I heard...$2.50 for a 12oz can of coke, $4.50 for a can of Bud Light, and $6.50 to $9.00 for a small mixed drink.... they could give you the cruise to get you on board to buy the drinks.
Number Four - a freebie - have fun, its the best vacation you will ever have