We've been on several, all but one in the Caribbean. My thoughts:
3 days is too short, two weeks too long, 7-10 days about right.
Enjoy the main dining area.
Seek out where the musicians are and at what times. It's surprising how good some of them are.
Spend the money and effort to take excursions in the daytime to see some things in each port. It's cool so get to see so many different things in such a short time.
We haven't been on one in about 5 years, its about time.
Edited to add, Get a balcony room.