We love SeaWorld, and were just there on 11/10.
For the older kids who will be riding the coasters, I highly recommend buying them Quick Queue wristbands. You can learn more about those on SeaWorld's website (although I see the page isn't loading this morning) -- you pay about $15 each and can go through a separate queue and get right to the front of the line. SeaWorld doesn't have many rides, so the queues do tend to get long. Although these are expensive, we found them very worthwhile. If your whole group is going to want to do rides, you might want to get them for everyone....
When you arrive (at opening time, I recommend), pick up the Quick Queue bands for those who will be doing the coasters and then head straight to the dolphin feeding area. They only let a certain number of people in at a time, and they only open it a few times during the day. You have to pay an additional fee -- I believe it is $7 per person -- and it is totally worth it. It is a wonderful experience.
Check the show times, which are also listed on SeaWorld's site. The two best are Believe (the Shamu show) and the otter/seal show (which is called something like Clyde and Seymore Take Pirate Cove). Arrive 15 to 20 minutes early for this one -- the pre-show is hysterical.
The next thing to know is that if you want to eat at the only sit-down restaurant, Sharks Underwater Grill, you can only reserve in-person, same day, and they open the reservations desk at 10 a.m. We enjoy eating there -- it is expensive, but the food is good and the view of the huge shark tank is outstanding.
The other queue that gets long (and the attraction you might all want to see) is the special Polar Express motion-simulator ride that's at the front of the polar bear/beluga whale exhibits. If you decide not to get quick queue wristbands, you'll want to do this right after feeding the dolphins (and depending on the show schedule).
You can also feed manta rays which is fun and doesn't require the purchase of more than one tray of food. Feeding the sea lions works the same way and is also really fun. The penguin exhibit is great, as is the manatee one.
SeaWorld is a jewel box. The park is well laid out, beautifully landscaped, and full of up-close encounters with marine life. It isn't possible to do everything in a day, but I've shared our family's favorites.
Enjoy!