Number 1. You need to master your diving skills. Not just get a PADI Open water certificate or the equivalent under any other organisation.... you need to dive, and the more the merrier and better. And once you master that, especially buoyancy, and start shooting pics... remember that safety is first. It's ok to skip a few photos in order to save your skin. There will always be another dive like that.
Number 2. It's a hobby which needs some expense to start (entry level camera will cost anything from €250 (but the second-hand market can be a steal!) and becomes more expensive the more you like it and want to add up on kit. Know your limit, work within it. Make a budget!
Number 3. Try to understand what's happening around you underwater. Talk to other divers, read magazines, learn some basics about the acquatic life, wrecks or environment you'll be diving in. If going abroad on holiday, do some research.
After those key rules, move on to the next...
Quite a few times, buddies and other divers ask me how can I learn a bit more about underwater photography?
I'm pretty much NOT a professional, just a guy who dives a lot and does lots of mistakes, so it's only tips from my experience and mistakes which I can provide... but also a few very good links.
The Underwater Photo Guide - One of the best sites around with tutorials, info, kit reviews etc. A must!
What are you waiting to become one? Unless you're into pensionable age (and some times as well), as long as you're relatively healthy, you can try!
In Malta, you have the option of either going to a commercial diving school (such as those affiliated with the PDSA), or else you may join one of the beginner's courses with local non-profit Scuba Diving Clubs such as Calypso SAC and ATLAM SAC. There are also some Scuba Diving instructors who although they provide training under the direction of a commercial diving school, they can provide one-to-one VIP service. Get in touch for some contacts, or look around.