Here is a nice site on sharkdive
http://www.martinsweb.com/sharkdive2004.html
I think there are some basic rules when diving with sharks.
(a) Get down to a sandy bottom very fast once you enter the water. Do not splash, - no backward roll, enter quietly.
(b) Keep a gear like a Videocam or a shark stick to drive them away if they get too close.
(c) Keep your buddy behind you looking the other way, so that 360 deg is covered
(d) Keep still and do not make too much noise to attact them
(e) Do not try to feed them, it can be really dangerous
(f) Don't dive with sharks with seals present around the area
(g) Bulls, Tiger, GW are dangerous in day or night and Reef sharks like white tip/ black tip etc can be dangerous at night when they feed.
(h) Wear chainmail protective suit if you are feeding sharks
(i) Shark repellant electronics are also available in market. use them if you need.
PADI/NAUI also have a shark diving speciality course.
http://www.kokanya.com/adventure/adven_divingB3.htm
(e) When getting back to boat don't hang around to much and do not snorkel with sharks around