I wrote a little bit about bracketing earlier, but it’s an important concept and it deserves its own entry.
You’ll often hear photographers talk about bracketing an image. Bracketing sounds pretty technical, but it’s really just a fancy term for taking multiple shots of the same image at slightly different exposures. With some scenes, it’s really hard to know whether you’ve gotten the exposure right, and it’s worth taking a few extra shots to make sure one of them will be good.
Let’s say that you’re shooting a scene and the camera’s meter thinks that the right exposure is f/8 and 1/200 sec. Maybe it is, but maybe that will result in a little bit of underexposure or overexposure. If you wanted to bracket one stop on either side, you could take one shot at f/8 and 1/100 sec, one at f/8 and 1/200 sec, and one at f/8 and 1/400 sec. Alternately, you could take one at f/8 and 1/100 sec, one at f/5.6 and 1/100 sec, and one at f/11 and 1/100 sec. Either way, you’d wind up with three images and if the camera was anywhere close to being correct you probably will wind up with one perfectly-exposed image.
In the days of film, bracketing was often a necessary but expensive operation. Digital cameras have made it cheap to take multiple exposures, since there are no film developing costs. Flash cards are both cheap and reusable, and you can fit lots more images onto them than you could on a roll of film.
Bracketing sounds cool, but I bet it also sounds like a lot of work. Want me to make it easier for you? OK, piece of cake.
All modern dSLRs have a function called automatic exposure bracketing, or AEB. When you enable AEB, you tell the camera how large an increment you want to use, and then whenever you press the shutter the camera takes three images– one at what it thinks is the correct exposure, one underexposed by the amount you specified, and one overexposed by the same amount. Click click click. You can usually specify the size of the compensation in 1/3 or 1/4 stop increments up to two full stops, sometimes three
Look at the specifications for your camera, and you’ll see something that looks like this:
AEB: +/- 2.0 EV, 0.5 or 0.3 EV increments
That means that you can bracket plus or minus two full stops, and you can choose either 1/3 or 1/2 stop increments. EV means Exposure Value, and it basically means the combination of aperture and shutter speed for an exposure.
Voila! All you have to do is turn it on, and your camera will do the work for you. Consult your camera’s manual to figure out how to enable exposure bracketing on your camera.
In situations where the lighting is tricky, I highly recommend using aperture-priority or shutter-priority mode and then bracketing your shots. This will give you a much better chance at getting a perfectly-exposed image.
Now, go try it out! Put your camera into either aperture priority or shutter priority mode, and enable automatic exposure bracketing. Find something well-lit, and take a picture. You’ll hear three clicks of the shutter, and wind up with three images. (It’s like a buy-one get-two-free sale.)
For extra credit, put the camera in manual mode, set the aperture and shutter speed to what the camera thinks is the right exposure, and then manually take three shots, changing the shutter speed to bracket by one full stop. Look through the viewfinder and check the meter before each shot. For one it should be right in the center, for one it should be one stop to the left, and for the third it should be one stop to the right of center.
Stop Shooting Auto! 
Patti, what is tricky lighting? When would be a good time to use bracketing? Would fireworks fall under that category? Or shooting a flying bird with the sun behind it? Or taking pics of bats in a dark cave at the zoo? Or is tricky lighting a subjective thing. As in… I’m such a novice that all lighting is tricky.
Fireworks are actually a pretty bad time for bracketing because of the way they show up in the sky. In essence, ou have to capture a whole burst in one image– you can’t shoot a second image of a particular burst, since it will already be gone.
Tricky lighting is subjective. It might be something where the light is changing rapidly, or there’s a huge contrast between different parts of the image, like a bright object on a dark background or vice versa. A flying bird with the sun behind it is definitely tricky– your camera is probably going to be tricked by the brightness of the sky and underexpose the bird. Sunrises and sunsets are excellent candidates, and you’ll often find that you like the slightly underexposed image better than the “correctly” exposed one.
It’s very rare for me to use automatic bracketing, but I find that I just instinctively do it in certain situations. City skylines at night are a prime example of when I do it– I’ll often shoot five and sometimes seven images for each shot. I know from experience that the camera’s meter is going to lie and try to trick me into overexposing the image, so I start at what the camera recommends and then bracket down from there.