Fly fishing Key West
I would start with Jeffrey Cardenas' shop in Key West, he can help you with what to expect to fish for and guides. There are some important things you need to find out when you choose a guide: (assuming you are a flyfisherman)
Make sure the guide is a real flyfishing guide, not a "light tackle" guide.
Ask what you will fish for, what kind of rods, reels, lines, flies he uses. (You want him to use top name brands)
Find out what kind of boat he has, make him describe in detail how it fishes, how shallow, dry, etc.
Ask about the conditions, weather, wind and heat.
You can not ask him too many questions, it's your money and more important it's your experience.
If there is anything else you think I may be able to help you with, please ask.