Plan, research, and balance: Plan what you want to do at each port before you board the ship- got copy of ships tours from Carnival or at least get a good Cruise Travel Guide Book of the Caribbean - Frommer's Foder's Berlitz, etc use a highlighter for things that you would like to do/see. Research those things that interest BOTH of you. At every port don't just go to the beach, vary your day trips on shore maybe including a few hours at the beach. Balance out your day with activity and relaxation that way you will not come home needing another vacation. If you plan to shop for souvenirs, do it at one port rather than every port. You can grab a t-shirt right near every port. On ship, encourage your partner to "do his or her" activity without you, so you will both have something to share and talk about later. At sea, relax, go to the dining room for breakfast or lunch as it is a slower pace and you may meet new people. Wear a smile and be happy, you are on vacation.