Move in. Light falls off much more quickly underwater than in air, so get closer to your subject than you normally would. Having a wide-angle lens with good closefocusing capabilities is a particular boon below the surface.
Forget the flash. Don't count on your built-in flash to add light. Since it's so close to the lens, it will illuminate any small particles between you and your subject (an effect called backscatter).
Check your white balance. Some waterproof cameras have more than one underwater WB setting because what's appropriate for a swimming pool differs from what you'd want while snorkeling in the Caribbean.
Get creative. When composing underwater, make the most of what you've got. In a pool? Try capturing the bubbles that form when someone dives in. Also try shooting up from just below the surface, as partially submerged subjects provide a perspective you'd never get on dry land.
Use the strap. Most waterproof compacts can be submerged only to 10-33 feet while maintaining their watertight seals. If you drop the camera, it might sink down too far, so attach a strap or flotation device. Want both? Olympus makes a floating wrist strap for its underwater compact models.
Keep it clean. Always rinse your waterproof camera in plain water when you're done, to clear out any chlorine or salt water.
Problem skin: Zap wrinkles or blemishes by positioning your main and fill lights just above the camera position (one right, the other left), overexpose, and reproduce the image as high-key as possible. Avoid side fill and keep your subject from smiling. Try a subtle-but-effective soft-focus filter, such as Tiffen's Soft FX 3 (from $40, street).
Bags under the eyes: Use front light only, with lights at eye level. Lift the camera slightly, and have your subject look up into the lens while keeping the chin down. Apply a little foundation makeup under the eyes, even on men.
Double chin: Shoot down onto your subject from slightly above. Ask your subject to lift the chin while looking up toward the lens, and position your lights as high as possible to throw the chin into shadow.
Weight issues: Lift the camera to eye level, and try to light the face exclusively, letting the body go into shadow. Crop out as much of the body as possible, and dress the subject in clothes that blend with the background. For tight head-and-shoulder portraits, have the subject turn slightly away from the lens, and light the far side of the face, so that the broader, near side of the face is in shadow.
Large nose: Shoot straight on as your subject looks directly into the lens. Light so the nose casts no shadow.
Speed up and slow down. Experiment with both long and short shutter speeds. Shutter speeds of 1 sec or more let you use the entire zoom range, producing pure abstractions, often with little or no recognizable subject. Shorter speeds produce an identifiable subject surrounded by dream-like streaks of color. With some subjects, either way works.
Control aperture. Small apertures (high f-numbers) produce thin streaks, while larger ones give you broad smears of color.
Go both ways. Try zooming in (starting at the widest focal length) and out (starting at the longest) for two distinctly different looks.
Use a tripod-or don't. You get straighter streaks and a stronger sense of structure when you use a tripod. Don't want structure? Handhold and move the camera left, right, up, down, in, or out as you zoom. To create a vortex, twist the camera as you zoom.
Shoot head-on. Record the object with your camera's imaging plane perfectly parallel to the primary subject planes. Whether it's a vaulted doorway, window casement, cornice, arch, or arcade, shoot it centered and straight on, without tilting the camera. (If you must tilt, follow the advice in "How to... Straighten out a skyscraper".)
Play up parallels. Place strong parallel lines in your subject parallel to the image edges.
Forget color. Try monochrome.
Look old. Tone your print to look antique with the sepia settings in most image editors, or by using Adobe Photoshop plug-ins such as Nik Software's powerful Silver Efex Pro ($150, street).
Filter it. Architectural details are one of the few subjects that benefit from Photoshop's Artistic, Sketch, and Stylize filters.
Group them. If a single detail is underwhelming, match it with a second (or third or fourth) image. Grouped images that share leading lines or dominant shapes can succeed as diptychs or triptychs, adding up to much more than the sum of their parts.
Speed up. Bump your ISO to 3200 or beyond-you want to get the shot, noisy or not. For a very young child, use thickwick candles, because three or four skinny birthday candles don't shed much light.
Preset exposure. Spotmeter a face near the lit candles, and then set that as a manual exposure. (Auto can be flummoxed in scenes like this.) Use a fairly wide aperture (f/3.5 or f/4) but one that gives you some leeway on depth of field. You want a shutter speed no slower than 1/100 or 1/125 sec-remember, the kid's going to move.
Hold steady. Tripods are impractical here. Use a monopod, tablepod, or articulating support such as the Gorillapod. No 'pod? Brace your elbows on the table or the back of a chair.
Set white balance. Use the Tungsten preset. This will keep the scene amber, but not excessively so.
Prefocus. Set your focus on the far edge of the cake. This is where most faces end up at the end of "Happy Birthday." And use manual-AF takes time to hunt in these scenes.
Shoot a burst. Start it early and end it late. If your camera can manage a decent number of RAW exposures in a burst, shoot RAW for more control over the image in editing later.