I've picked up moorings in Annapolis many times -- at least 2-4 times a year -- because I love it down there, and it's an easy sail from where I keep my boat. The moorings are laid out pretty well in a grid, and there is only one size. The mooring penant is a heavy line about 6 ft long with an eyesplice at the end, and it has chafe protection as well. So follow what the above folks have suggested and you'll be fine. I do it single-handed all the time.
The first mooring field you come too, the one right at the mouth to Ego Alley, can be rough with a north breeze. It's fairly open to the N and NE, plus all the chop from the MANY boats going in and out. There's another mooring area above the Spa Creek bridge that is more protected. Both areas have water taxi service if you need it, and a pumpout boat patrols the area as well. There are several dinghy docks scattered around if you need those.
Also, the harbormaster will be there in a jiffy to get your money.
Both the moorings and the slips on Ego Alley itself are first come first served. In my experience there, more people use the moorings because they are much cheaper than the slips. Annapolis is redoing the slips right now to make them wider, but that should be finished soon from what I hear. They have been a tight fit even for my 33 footer.
You can get a 10 lb. bag of ice for $2.50 from Storm Brothers Ice Cream Parlor. Look for the red and white striped awning. Have breakfast at Chick and Ruth's about 8:30 during the week, or I think 9:30 on weekends, when the owner leads everyone in the Pledge of Allegiance. During the week you may likely see former Gov. Mandel having breakfast in the booth that normally is roped off. There's more generous seating up the stairs in the back. You may know all this already, but here it is just in case.