This was my first cruise, and I went alone. I am single, age 35. Carnival was practically made to order for my situation. I have decided I will definitely do this again next year, and it will be Carnival to some warm location.
I flew to Miami, stopping in Atlanta, and took a shuttle to the port. The porters are not employees of Carnival (nor airline personnel for that matter) and I recommend packing fragile things well--it is best to assume the luggage will be thrown and dropped when you pack. Happily, I had no damage myself.
Embarking took some time, but not that much. There was very little standing in line if you have a preprinted fun pass--I walked right by a medium-long line of people who didn't have that. I received my Sail and Sign card, which is the shipboard credit card as well as the room key. I recommend learning your room number--it is easy to forget to do that in all the excitement, and several people I met did. I actually got one digit off and had to try two doors to find mine. Luckily, if you buy something, the receipt will have your room number printed on it.