I worked in the cruise industry for 15 years in sales doing new ship introductions, etc and have cruised all over. Alaska, Caribbean, Mexico, Italy/Croatia, South Pacific and Australia.
Lookout pretty much said it all. You have to go through the mandatory "how to jump off the ship as it goes down" to-do on the first day.
Definitely go to formal dining at least once. Formal night is the best time as that is Lobster night.
And truly, if you want seconds/thirds, it's yours. Just ask.
They'll want to take your picture everywhere. Getting on the ship, off at each port, at dinner, on formal night, etc and then sell them to you. Head to the Lido Deck when you first check in for a buffet lunch. And yes, get there early. It'll give you time to acquaint yourself with the ship.
The shows after dinner are pretty good. Prior to dinner, find a nice bar that you like for cocktails ahead of time. Don't lose your cruise card as you will need it getting on and off the ship and for purchasing drinks to. It's a royal pain if you do.
Your room stewards are phantoms. You leave your room, forget something, come back in a short time and it's all neat and tidy. Hopefully you have a veranda. The only way to go!
The tips for drinks are already included on your bill so don't tip again.
And....have fun!!!