Doug, there are some tips that can be useful for you, I'll try to give you a piece of advice:
I'ts a good thing, specially in the beginning, that you take macro and close-up pics. Wide angle is more difficult, and if you start with uwderwater scapes, wide angle scenes, maybe theese first photos won't result as nice as you expect. Many people could feel dull with theese first results. But if you start with macro it's very likely that you get preety shots in a few dives.
Begin with small subjects (not too small, for very little things yo need another kind of lens), still critters, so you can stay very close to them and hey don't go away. Go as near as you can, and when you have the subject focused, shoot. You will obtain a nice close up image.
When you want to get a close up pic, and don't have an external stobe, it's useful to do this: get very close to the animal, NO zoom (not at the maximum I mean) ; so you are compelled to stay close to it, and the inernal strobe of your camera will enlighten the subject because your strobe is close enough to it. The colours will be better and you will like your pic a lot!
If you have an external strobe you can shoot from more distance because light will reach the subject anyway. And you can use the zoom in order to get a close up of the animal. But if you are working only with teh internal strobe you need to stay "physically" as near as possible because the light of this strobe is not powerfull enough to reach subjecs from big distances.
Another tip: subjects don't look nice if you shoot from an upper level. And shots look quite bad taken from behind of the fish. You must try to place yourself at the same level of the animal, or even a bit lower down. And in front of it or at one side of the fish, slightly facing it. But try not to photograph from the animal's back, it will cause the sensation of the fish swimming away from you, and that's not the effect you whish.
Try to get an entire image of the animal, I know this is hard because fishes move around very quickly and sometimes you cut the head or the tail in your pic. If you find it difficult, you can also take a shot of the face or the first third of the animal's body, I think that it's easier, at least for me.
As I've said before, it's important to play manual controls: F and shutter, basically. A higher F value will darken the shot. A smaller shutter value will darken it too because the light passes very quickly through the lens. So if your subjec is very clear, there's a lot of light arond you or you are too close to the animal, it's good to select a higher F value or a smaller shutter value (for example, 1/200 is faster than 1/80, it provides more darkness). Be careful with this, because with slow shutter values, fishes can look non-focused and blurred. If you are shooting a moving animal, you can keep a small shutter value (a faster one) and decrease F number in order to obtain more light for your photo. Well, that's very general, you should try with different values and see wich are the most suitable for every case.
We can resume this: search the best balance between F and shutter to obtain he correct light, not too clear, not too dark. With some practise sure you will get the hang!
And remember: go as near from the subjec as you can. At the same level or slower down, and never from behind (exception: if you see a whale shark, sure it will look great however you shoot it 
)
Ok, hope my advices could be useful for you, go to dive as often as possible, that's the best way to improve in diving and in photography too! Regards, and good luck! 
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