Our first cruise we arrived around 11. Much of the crowd was still in line checking in so it was easy to get back to concierge. Then, as pp mentioned, we entered through the side door to board. We weren't the first on board as check in took time.
While the port opens at 10:30, people line up to get in well before that. Unless you take a
DCL bus, there's really no way to avoid that line. And if you want to be at the front of it, you probably need to be there by 10. If you want to avoid all the lines, arrive closer to 11:30/12.
Are you driving yourself? Many of the transportation companies won't even offer to drop you off before 10:30/11:00.