Ditto on what Dave said. I would definitely recommend getting on board as early as possible and eating at the Windjammer (AKA, the buffet) first. By about 1:00 (or sooner), the buffet will be absolutely packed, so get there early, eat, and get out of the way so the next person can get in. The crowd at the buffet on embarkation day really gets frustrating at times. A lot of families and large groups tend to use the Windjammer as a place to catch up on old times and it really creates a mess. Besides, the food at dinner in the dining room will be much better anyway and you can take your time there.
Another key point...when you arrive at the pier, you will drop off your luggage (bring at least a few bucks to tip the porter) and won't see it again until it is delivered to your stateroom and you may not have access to it for the bulk of the afternoon, so make sure and bring a carry-on bag specifically for the ship with your swimwear (if so desired) and possibly even your dinner clothes, if you are scheduled for the early seating. Sometimes, especially on the bigger ships, it can take forever to get your luggage delivered to your stateroom.
Good luck and have a wonderful cruise!!!