My son took two cruises with us before he was 2 years old. This was about 10 years ago, but much still applies.
Definitely tell the cruise line ahead of time that you will need a crib. Have your TA request it as soon as possible.
As to what to bring, the items that top my list are medications (ships do not stock children's versions, and you may have problems finding these ashore) and a few favorite toys for the cabin. Also, as with any trip, bring at least twice as many diapers you would normally go through in the same number of days. And, scented diaper disposal bags.
Prepare your child for the dining room by gradually introducing him/her to eating out in nicer places at home. Do not feel you have to miss out on the formal dining room because you have a child. So long as s/he knows what to expect, things should be fine. We started out by eating every meal at home in our dining room as a family, then worked our way up to diners and nicer restaurants. Once on the ship, order an appetizer for your child. Even carrot sticks or celery would do. There is a tendency for waiters to bring the kids' food out early so that s/he doesn't have to wait while you're on your appetizers, but then the child has nothing left to eat when you are on your entree, and then becomes bored.
Also be aware that your child will not be able to use the swimming pools onboard due to health regulations.
The most important thing to realize -- and I think you already have -- is that this is a family vacation and not a romantic getaway. That's the key to enjoying a cruise with a baby or young child.
I'm sure I'll chime in with more tips as I think of them.
