There are a couple of people on YouTube who give good advice.
Emma Cruises - fairly young woman who does cheap cruises. Has a thing about cookies.
Tips for travelers - a more mature gentleman who has a thing for afternoon tea and cruises in more luxurious settings.
I'm slights addicted to both, even though I would never go on one (I don't like being on water, I would never sleep).
Tips for travelers has lots of information about drinks packages, when to upgrade your cabin, which cabins to pick ie not underneath the disco. One the upgrade, you can be offered an upgrade but although your cabin will be 'better' you might have a view of a life boat, or be right at the front or back which experience most movement.
Will you be in one cabin? If not try to get connecting doors.
Things like spa treatments are cheaper when the ship is in port.
One thing I would check (because water!) is whether the ship can dock in port or whether you have to make the trip by small boat.
Enjoy yourselves. Oh and get 'cruise insurance'.