Study about sharks before you go out to swim with them. Go to the library, or book store, to view the latest shark books. Summers are a good time for "Shark Week" documentaries to watch, too.
Look for a tour company that specializes in swimming with sharks. These companies have people that specialize in sharks. Your best bet is to swim with sharks in an aquarium, protected by a suit and cage.
Get together with the shark expert before you swim with the sharks. Receive your safety brief as well as your underwater suit, including helmet. Ask questions as you're going to be underwater dealing with creatures in their own element.
Start swimming. Get lowered into the water and listen to your expert's voice for instruction.
