I thought you just got on the boat and off you went - but it looks more complicated than that.
But in reality it is NOT complicated

Disclaimer: I have been on 15+ cruises - most with Disney
Things to "Work" on
Where to Go: Bahamas, Caribbean, Alaska, Europe, other
How Long: Kind of depends upon where you go
When to Go: Bahamas and Caribbean all year, others are "limited time only" cruise
Which Ship: when and where will determine the ship taken. All of the ships are very nice. The oldest ship is the Magic, but she had a major overhaul a few years ago, the Wonder is a year newer than the Magic and retains most of her "classic" features. When totally full these ships can sail with about 2500 guests. The new, larger ships are the Dream and Fantasy. They have some "cool tech" and additional features over the classic ships (but their staterooms are smaller than the classics).
Room Choice: Inside, Oceanview (porthole), veranda ("enclosed", solid wall or plexiglass), or concierge room. The higher up you go the more you motion of the ship. same with way forward or aft. Very much a personal preference. the question that you have to ask yourself is: how much time do you spend in the stateroom. For my family, we use it for "naps" between 1am and 7am (yep we go go go and then relax on deck somewhere), and to shower and change clothes between our daytime activities and dinner / nighttime activities. We have had a veranda a couple of time and it is NOT a big deal for us. Not even in Alaska.
Port Adventures: Do you want to do something at the ports of call? Do you do a cruiseline sponsored excursion, find a shoreside operator or go totally on your own.
Picture Package: do you want to stand in line and get lots of pictures with the characters or the backdrops. If yes you should consider purchasing the photo package before boarding the ship to save a little money.
Adult Dining: Do you want a fine dining experience outside of the main dining rooms? If yes there is brunch in Palo on sea days, Dinners every evening, and additionally on the Dream and Fantasy there's Remy's which offer the brunch and dinner as described. Cost per person: Palo $30+, Remy $80+. you can only book one brunch and dinner online pre cruise. I don't know if you can book both a Palo Dinner and a Remy dinner - haven't tried that.
Getting between the Airport and Ship: DCL does have convenient transportation and luggage. It's a little "expensive" but not really. Convenience IS worth something. I usually take DCL transfers - I like the "previews of coming attractions" video with Mickey and the gang that they show.
Things to Not Worry about
Dining Rotation for dinners: you will be assigned a different restaurant each evening, have an assigned table. It will either be Main (around 5:45) or Late (around 8:30). Your tablemates and serving team go with you from restaurant to restaurant
Breakfast, Lunch and Snacks: the buffet will always be open for breakfast and lunches (closed between changeover between breakfast and lunch) and quick snack locations are open from early to late. The free drink station is open from early morning to late at night with Soda, water, coffee, tea, hot water, hot chocolate.
Room Service: most items are free - sodas delivered carry a charge. I've NEVER used this - there's enough food elsewhere on the ship
Entertainment: the main stage shows are free and your seating time is opposite of your dinner time. And there are "family shows" between the dinner seatings that are very enjoyable. And then there are all of the other activities scheduled throughout the day.
Kids Clubs: Children between the ages of 3 and 18 have a spot "reserved" for them in the various clubs
What You Need
Money - and Lots of it!!! - and that just gets you onboard - more costs to come ...
Money for Gratuities: This is how your serving team and room steward gets paid. in the past (there's a hint of changes coming industry wide) it works out to $12 per GUEST (even infants) per NIGHT of the cruise. so for 3 guests on a 7 night cruise the expected gratuities charged to your room will be: $12 * 3 people * 7 nights = $252. You don't have to leave extra for breakfasts and lunches, this covers it all. Some give less many leave more based on your service received.
Money for Shore Excursions: you DCL booked shore excursions are not charged to you until you board the ship so they will go on your onboard account
Money for Souvenirs: there are several shops on board to buy stuff that you can't live without
Government Issued Photo ID: for Caribbean and Bahama cruises you only need a Official Birth Certificate and photo id (for everyone over 16 or 18 years old). IMHO Passports are much better to travel with. All other DCL cruises to date require passports. Bring your drivers license even if you are using a passport - easier to hand to security when reboarding the ship in ports of call.
SUN SCREEN: for most cruises - because the sun IS Different (much more intense) in the caribbean and bahamas than where you live!!! Just say NO to sunburns!!!
Other things
Personal Navigator: In the Port and then every night you will receive the - will list the next day's activities and times dining locations are open
Ticketed Events: there are more ticketed events scheduled from Character Gatherings to Mixology. Some are free, some carry a charge
You Can't Do It All: so don't try, don't stress. That being said, sleep is for AFTER the cruise
You Can't Eat It All: But this is the time to try new / different foods. If you don't like something, they will bring you something else - no additional charge so it's kind of for free (see MONEY above)
Take the Stairs NOT the Elevators: you get to eat more desserts this way - and will usually get to your destination quicker than waiting.
heck, there's probably a lot more stuff to consider, but this should give you a good overview of what to expect. The cruise is not like planning a WDW vacation: Hotel, which park which day, what fast passes, dining reservations 6 months in advance, early magic mornings/evenings etc, etc, etc.
Good Luck and Have Fun!!