if you're like most people with digital cameras, you look at the pictures you are taking on your camera's lcd screen just after you've taken them to assess if you've exposed it correctly. this isn't really considered cheating but it is known as "chimping". chimping basically means that you're not trusting yourself to expose your image correctly but instead are relying on your screen to see if it looks right. why is this a bad thing? well lcd screens can vary in brightness and can be somewhat unreliable. plus the images on the screen are significantly smaller making it difficult to get an exact idea of how successful the exposure really is. if you've ever finished taking photos and then after downloading them to your computer have noticed that they appear lighter or darker than they seemed while taking them, you have experienced the unreliability of this approach first hand.
so what do you do?
learn to use your histogram.
here are a few tips on how to read a histogram:
the whole histogram shows the various levels of dark and light values present in the specific photograph. the left of the histogram graphs the dark values and the right of the histogram graphs the light values. this ranges from very dark, to dark to medium, light and very light. when the peaks of the histogram are higher on a specific point of the graph, there are more values present at that tonal value. the main thing you want to avoid when using your histogram is the loss of too much information in your highlights or the lack of information in your shadows. histograms can assist you in keeping your photos properly exposed.
above is a histogram of a photograph that is completely overexposed. there are hardly any values at all showing in the image. you can have histograms that favor one side of the spectrum, while still maintaining proper exposures.