An external flash is a great tool, a valuable asset in a dSLR or advanced compact owner's camera bag, and the more you can control the light that comes out of it and that hits your subject, the better your photos will look. A flash can really enhance your photos and lend to your creativity. While a straight-on, automatic flash will yield a perfectly acceptable image, external flashes have the ability to yield beautifully lit, professional-looking photographs with a little tweaking. Here are five things you can do to get the most out of your external camera flash.
1) BOUNCE IT: For most indoor shots, the addition of some bounced light from your external flash will enhance your photos. Angle it toward the ceiling, giving you a large light-colored surface to reflect down off of, creating a giant pseudo soft-box. Rotate it to the left or right to bounce it off a wall; angle it and rotate it into a corner. Try some different things, and see the results of the soft, diffuse light it creates.
2) REFLECT IT: Sometimes due to high ceilings or being outdoors bouncing the flash is not an option, but you can reflect it to reduce the harshness of direct flash. Some flashes have a white card built in that extends out from the top of the flash head, so that when the flash head is pivoted up there is a surface for it to bounce off of toward the subject. Although these cards are small, they are very convenient. There are a host of products on the accessory market that attach to your flash that provide a surface to bounce off of. An old trick is to use an index card and a rubber band, pivot the flash head upward at an angle, rubber-band the index card to the top of the flash head so that it extends out above the flash tube, and you have a great bounce card.
3) DIFFUSE IT: Bouncing and reflecting can provide a very nice, soft light, but sometimes you want it to be more directional, to have more control of it; then you can use a diffuser and still have the flash head aiming directly at the subject. This is generally a milky, translucent piece of plastic of some sort that goes in front of the flash tube to diffuse the light for a softer look. Some flashes have a diffuser panel built into the front of the flash head that pulls out, or sometimes one is included with the flash in the box and snaps on the front of the flash head.
There are a variety of aftermarket diffusers, from simple ones that just slide over the front of the flash head to some that resemble miniature soft-boxes and Velcro onto the flash head. All of them can be easily removed and do not take up much room in your camera bag.
4) COMPENSATE FOR IT: Your external flash, in conjunction with your camera, has a rather sophisticated flash metering system that works very well...for most things. Sometimes you might want to reduce the output to just a touch of light on something, as for a portrait out in the sunlight. Even your camera's auto fill-flash might be too much light for a natural effect, so use the flash exposure compensation to reduce the output a little. There are times such as with close-up work that you want more light than the flash thinks it needs to put out: just dial up the power with the flash exposure compensation. It allows you to increase the flash's power output while still enjoying all of the benefits of the flash's automatic metering.
5) TAKE IT OFF: There are only so many things you can do with your flash in one position, on top of your camera, so take it off the camera. Your flash will need to still be able to communicate with the camera--some cameras and flashes are capable of wireless flash, but for those that aren't, most camera manufacturers make an off-camera hot-shoe cord.
Wireless flash permits great flexibility in positioning the flash, whereas an off-camera flash cord will only give you a few feet, though that is enough to achieve nice results. Off-camera flash is very beneficial for portraits and macro shooting: the flash can be raised up high and to the side for a nice single-light portrait.
When shooting macro work like flowers, the flash can be held in the hand and easily moved around to get the most light into the subject. If you have a wireless camera and flash combination you can even add a second flash into the mix to be controlled by the camera in conjunction with the first one, for a fully automatic, wireless two-light setup.