Once you arrive at the port and check in you will receive your boarding #. Your boarding # is tied to your PAT (Port Arrival time) that you will pick when your booking window opens. If this is your 1st cruise you can do this 75 days prior to your cruise. Concierge Guests and Platinum Guest get boarding #1 (and sometimes 2)
They usually start boarding 11:15-11:30 for the Dream and Fantasy 11:30-11:45 for the Magic and Wonder. Once they start calling #'s it goes very fast with the new # being called about every 5 minutes. They usually go to open boarding (you don't have to wait for a # to be called) about 12:30.
Once you start to board they have a place to stop and get your picture taken with a Disney themed backdrop. This usually backs up a little. You don't have to do this and can just walk around this area.
You will enter on deck 3 (Miami is deck 4) and they will direct you to one of two restaurants. Both are buffets. The one on the 3rd deck will have waiters that will bring your drinks to the table. The other restaurant is on the pool deck you will need to get your own drinks but can take your food out by the pools

. They ask that you don't save seats by the pools. By the way be careful this is a VERY HOT topic on these boards. LOL.
When you check in you will receive a Navigator (Newsletter) or there is an app you can download that will list where to pick up tickets for the Princess meet and greets, wine tastings and other events. If you don't see what you want stop by Guest Services and they can help you out. Many of these thing need to be booked the first day so don't wait.
Here is a link to past Navigators so you can get an idea of what they look like.
http://disneycruiselineblog.com/personal-navigators/