Personally, I didn’t find shooting wide angle underwater all that difficult. It is actually quite forgiving. A: You have a huge depth-of-field (area that will appear in focus in your pictures). B: It can eliminate a lot of the scatter in your viewing area that can clutter up your pictures or cause several unwanted lens flares. C: By using your lighting/strobe in a creative manner, can open up some dramatic possibilities for prize winning photos.
Distance/Composition: Get as close as you can. You can get as close as a foot away in many cases. Looking through your viewfinder or your LCD screen, think of what you are looking at as a poster. How would you like to see it? You start with your main subject in a lower left or right corner. Then you look at the surrounding area to provide a picturesque scene as your backdrop. This can be anything from the abyss, more of the reef or a school of fish. Showing the bottom of the boat at the surface can add affects. I use the surface light (sun) on a frequent basis.
Light Source: Wait…we just established that? No we didn’t. You only want to use the ambient light if you are shooting available light only. 
I will shoot with available light occasionally on wreaks to create a “mood” in the pictures. Otherwise, you fire the strobe. This is what can make or break the shot. Spotting the light where you want it is key. I use a modeling light mounted on my strobe to help with my “spotting”. That spot should be your main subject. I always use the “High Power” setting on the strobe and have it on an extended handle so I can get it well away from the camera and creating a unique angle lighting my subject. You think ahead in a manner of speaking. You have a perception of where shadows will form to accent the image. If you are shooting with digital, you have the luxury of looking at your image on the screen affording you more creative options of changing angles, distance and cropping. If you are shooting film, bracket (taking several pictures with different light angles distances and direction). Every time you snap another picture, think about what you are seeing in the viewfinder. Look for that spot of light from the modeling light and imagine the lighted shapes vs. the shadows. It can give you ideas for that very next shot more often than not.
Model: My wife, an excellent diver, dive buddy, scout (she also helps find several of my subjects) and model appears in several of my pictures. A human in the picture gives the viewer size comparison. 
The model can make or break the shot also. Does the model exhale as you are taking the shot. That can create a cluster of bubbles totally obscuring the face. A good model learns to slowly release air to create a desirable stream of bubbles trailing behind her. No bubbles is acceptable. Sometimes, another diver just a little farther back adds more interest as long as they are doing something relative to what’s going on. Example: If the main model is observing some pillar coral, the other is close by making the same discovery with interest. There should be some distance creating size differences between the two divers.
The model should concentrate on their form, keeping legs extended with slight bends in the knees, arms at sides, breathing correctly to control bubbles, and affix those eyes (as they are often visible in the images) on what is presumed to be the main subject. All of these items add up to making a good picture even better.
Let’s come back to distance: With your main visual being very close, the diver should be approximately 10 feet away swimming over and just behind the main visual, at least as a starting point. Now, whether they need to be closer or farther away is creative judgment by you, the photographer. This type of shooting requires team work and good communication. Discussions on the boat are helpful. Let each other know what was done correctly as well as wrong. You want the good stuff to be made into mental notes so you continue to do them correctly. Click on these images in the “Scuba Photo Art” library to see the techniques used to achieve the results.
