Oh, you'll love it! I adore the cruises! I don't know much about the magic sadly, even then it's Disney and they rarely fail to make and enjoyable experience!
! As everyone else said, bring the medications! Oh, my trip would have been miserable if my family had not had any form of medication! That is probably the #1 got to have... Other than clothes....
Bring extra clothes, this is a "no duh" for any vacation but trust me, you'll see why. Along with clothes, bring some warm stuff, jackets, maybe a sweater, etc. Febraury is certainly not warm and the breeze of the ocean can be quite cold, you'll want it.
Last but not least you will want to bring some fairly decent, nice clothes for the dinner. I am not aware of what the Magic requires for their nicer restaurants but, just in case, maybe bring that nice blouse.
Have fun getting use to a rocking boat! I know the ship is gigantic but that does not mean you can't feel the boat sway. When your off the ship, your walking will feel very bizarre. Just a heads up.
Depending on the length of the trip, don't attempt to get everything in at once! You'll get bored eventually if you already crammed everything in. Just relax, enjoy the time being away.
Meet people, it can make the trip more enjoyable. My parents meet a British Family once that made the trip so much more worthwhile. The only thing I must say is, this is certainly not a top priority, it is that I want you to be open to meeting people. If you have kids, encourage them too.
Late at night is a great time for a walk. No people, kids, or noise. Just you, the ship, ocean and the fresh air.
Be open. Try new things. It's Disney, there no reason to worry if it may kill you. Try interesting food and stepping out of your comfort zone.
Use Port Adventures (on ship) to plan anything you want to do at the ports. It ensures what you can do and trust while you're there. Things can get expensive though so watch out!
Beware the stairs! I remember I was on a 3 day trip to the Bahamas and twice, TWICE, I had to go from deck 2 to deck 11... 11! Since Magic has fewer floors, I wouldn't worry so much but, even then, it is tiresome. The only reason I had to go twice was because, they thought it'd be a great idea to check maintence of the elevators, twice, in 3 days. *Sigh*
Don't over pack. Take what you need, not what you want and think you need. You'll hate packing it all back together. Your room is small you'll want all the space you can get.
Pictures. You will want to remember these moments.
Don't over drink. A hangover is already no fun, do not let it ruin your vacation.
Trust you gut. When you feel that something is unsafe, it probably is. (This does not mean I don't want you to step out of your comfort zone!)
Last of all! Enjoy. Don't worry about the pets, or your home. Enjoy and relax! It's vacation, let Disney do it's job!
Good luck! My Mickey Friend!