Lucky girls! I love cruising, I've been on several though it's been years since my last one. Also, I've never been on a "freestyle dining" cruise ship which I think I'd prefer since I don't like being forced to eat at a certain time. Will you have that on your cruise?
The only advice I can give is you might want to research your ports of call in advance and skip the expensive (and often mediocre) shore excursions and hire a taxi to take you where you want to go. We had the best time in Mazatlan and in Bermuda when we did that. Though I guess maybe if it's just the two of you you'd feel safer on an organized excursion - ?
Also, be prepared to be bombarded by the cruise line trying to sell you something on board, happens constantly. Same thing on their shore excursions, they always take you to shopping places that have a contract with the cruise line at some point on the excursion. And be prepared to EAT like you've probably never eaten before! lol
Have a wonderful time! I'll try to think of some more to share.