You are going to love all the reef dive locations around the City of Key Largo. Horseshoe reef is a winner, plus good for beginners, as it is located nearer the shore. Newbies tend to like to see the land, and the reef area is close to other notables you can also do: Elbow Reef and Dry Rocks. This is mostly a long straight reef, and nice and shallow for a quick morning or afternoon dive.
You want to pick a fine day with big sun and good visibility, that will reduce the problems beginners might have. It does make you more comfortable with a nice weather day. If you are here for a week it becomes much easier to pick out the best patch of weather. For weekenders from Miami, just pick hotels with good cancellation policies and you can just cancel and rebook for the following weekend.
More newbie-beginner scuba locations in the Upper Florida Keys we like are Grecian Rocks (Great shallow water dive spot ranging from 5 to 25 feet) and the Hens and Chickens area (Nice and shallow at 5-25 feet, with loads of critters, sharks, and coral). And for breakfast you will have to try out the Big Breakfast Burrito at DJ's Diner. This has three scrambled eggs with cheddar cheese, salsa, sour cream, with potatoes, and golden fried hash browns.
The captain will put you in some clear and warm reef waters. Examine lots of coral reefs on your dive trip, starting about 15 minutes from shore. Plan on seeing lots of corals, such as star and brain coral. The reefs have octocorals, like sea fans and sea plumes. We saw so many different types of marine plants and animals.