I don't have much to add to what Jen and Michelle have said. We arrived a bit later last time - but it didn't matter. We got dropped off, left the luggage with the porter and DH parked. We went through security (medium line) and up to check in. I got to go to the
Castaway club line (returning guests) and it took about 10 minutes with having done online registering. I had DH's passport with me. We were done before he came in. He had to get his picture taken separately (just before you go on the ship). We had ours done at the check in desk.
Do as much online as you can. including register your DD for the club. You'll still have to get her the bracelet, but you can do it at the terminal or on the ship later.
The line for kids' club bracelets was long and we got called to board before we got close to the front of it, so we did that in the afternoon. Had lunch - room ready by 1:30, which was when we finished eating. Just explored the room (so cool!), checked in the kids' club and got bracelets there. We did not swim that afternoon. Just explored the ship. It is open house during the afternoon. If I recall, the shops open after you leave port.
We had late dinner, so we hung out after the muster drill and saw a bit of the sail away party. That's a fun time!
There's not much reason to get to the port too early. If you hate standing in line, you could be first, but you'll just be waiting at the other end to board. They have never boarded anyone before noon on the three trips we have taken. No matter what you do, there seems to be a lot of waiting. There's just so many people!
In the terminal they have a character meet by the cruise ship model and there will be a line there too.