Improve your Underwater Images
Taking spectacular underwater images is not difficult if you follow a few simple techniques. The following tips will ensure you get more than your fair share of compliments for your underwater images.
First of all you will need a camera and housing. Choose the camera, housing, lenses, and strobes that will achieve what you want to do with your images. Most often the deciding factor will be your finances or lack there of. Max out your credit card, empty your savings account, trade in your car, whatever it takes to get the best equipment you can. As soon as the photography bug bites you will want to upgrade your equipment again and again. There are unlimited options with regard to purchasing photographic equipment. Talk to your camera retailer, dive shop, other underwater photographers, and surf the net. There are many considerations so only you can decide what will be best for you. A 15 or 20mm lens for wide-angle shots or perhaps a 100mm macro lens for close up shots. No strobe, one strobe or two strobes, perhaps a built in torch for night shots, the options are limitless.

Tips
Get as close as you can to your subject. The less water between your camera and your subject the clearer your shots. It will also limit the blueness in your images. Subjects will appear only various shades of blue when taken from a distance of greater than approx 1.5m. You will also achieve better focus in your images.
Sea-water absorbs red light and your images will improve with the colour-restoring properties of a Strobe. Strobes also limit the amount of backscatter in your shots by illuminating your subject at a different angle to your lens. Backscatter is unwanted spots that appear in your shots, usually sand, silt, or debris floating in the water that are illuminated by a built in flash.
Shots taken with the camera facing the ocean floor can be quite uninteresting. Turn your camera upward so that your shots have a uniform blue background.
Shooting upward with the sun in your images can add interest, however be careful that it does not detract from your subject.
Sit quietly where possible (ensuring you do not to injure the reef). Fish and other marine life will often approach you out of curiosity, allowing you to take as many shots as you desire.
Try to focus on the eyes of your subject, that is where your eyes are naturally drawn, when looking at photographs.
Dive with a guide. They know where all the good stuff is.