Digital Photography School did a good post on 5 Rules in Macro Photography and When to Break Them. I thought it was pretty good, especially since in underwater macro we have our own rules.
Black Backgrounds
I admit to being a partial nut on low-key underwater macro and even made a video and wrote a blog post about it. Low-Key is relatively easy to do underwater because you don’t have much light to use anyway, so you might as well keep the darkness as a background.
However, sometimes color, whitewash, or high-key photos work too. Look for white or bright backgrounds or bring your own.
Some people I know also bring slates with a color scheme. That way they can get a disco-glitter background. Combine it with bokeh (blurry background) and it gets really “dreamy” really fast.
Frontal Face Shots
if you are having trouble choosing a macro shot, just get in front of the subject’s “face” and get as close as you can. This is the “never fails” shot. But if you’ve seen 5 million photos like this, it starts to get a little bit repetitive. And sometimes the subject doesn’t cooperate: you can’t get in front of it.
Instead, try other aspects of the subject like feet or gills. On frogfish, the feet are absolutely fascinating to capture. Nudibranch gills look like feathers and can save your dive if all the nudies happen to be “head-down” in the rocks. Try to get your friends to laugh about the phrase “nudi butts”.
Focus on Rhinophores and Eyes
Another general rule is that the eyes or rhinophores (eye stalks on nudibranchs) should be in focus. Mostly this is because the human eye always looks for the eyes of other humans: “look at me when I’m talking to you…”
However, if the subject has other prominent features, then it makes sense to put them in focus and the eyes in half-focus. Things like crab claws, nudi butts, coral polyps, etc make great parts to be in focus.
Fill the Shot
In general, you want to fill the shot with the subject. That way, it has more detail to show.
But sometimes it’s very nice to leave a lot of negative space around the subject, especially if you use low-key or high-key techniques. That balances out the shot.
See you underwater!!
–Mike