Ryan,
You might also like to read this post I made ...
Claustrophobia, SHARKS and FEAR!!!
Btw, this isn't any kind of earth shattering wisdom but here is how I like to explain things to people.
1) Respect - respect your environment and realize you are not in YOUR backyard anymore, You are in THEIR house (the sharks, rays, fish, etc).
2) Common Sense - If its ugly and has LARGE FANGS don't stick your arm down its throat, hehe. And even more importantly, some of the most deadly creatures on this planet, both underwater and above, are very "pretty" and not at all ugly with fangs. #2 kind of goes back to #1 again.
3) Think - remain calm and focused. The most dangerous thing in the water is YOU (meaning humans). Most creatures, big and small, would rather get out of your way than tango with you at Davy Jones' Locker. Even if you come across a MAKO having a bad hair day - DO #1, USE #2 and SHOW #1
Something to remember - And I will use La Jolla, CA as an example for you. Most people don't realize that if you put on your mask and stick your head under the water in only knee deep water you will (not only look like a goof ball but) notice there are SHARKS everywhere, and the last thing they want is for the JOLLY HUMANOID GIANT to step on them!
Now, add some long Floppy leg Extensions (fins), a bulging Chest plate (BC), strap a huge chunk of metal to your back (tank), let some long black Tentacles that scream with air like a banshee flop around you (Regulator hoses), stare with a large single eye like a Cyclops (mask) and a protruding single horn on the side (snorkel) and what do you have? ... YOU ... and you're one big large funky scarry looking creature to most anything you come in contact with (again both under and above water, hehe).
My point is you look like a BIG scarry creature to the underwater life and the first thought in their mind is NOT "hey lets go mess with that thing". You are now a couple of feet thicker and longer than normal and you can usually be assured they are more scared of you than you are of them. This included sharks for the most part. I just love to see people get all freaked out and walk on water to the shore with stories like "There was all these 3 - 4 foot long sharks circling me!!!" .... Well, of course they were silly, they wanted to keep their eyes on you at all times, they are afraid you're out there to make them your lunch!
There are exceptions to most all rules but for the most part the "Law of the Ocean" is a lot like the "Law on the Land".
Meaning, if you look like Pee-Wee Herman, you most naturally don't go around looking for the closest thing to Arnold Schwarzenegger you can find and pick a fight with it! You wont live to long that way! Same thing in the water. Remember, you're the stranger in the water, and they will either want to keep an eye on you or they just want to get the heck out of dodge!
Anyway, I think you get the point. If done properly, Scuba Diving is one of the safest hobbies you can do.
=-)