An extremely useful editing tool for adjusting brightness and contrast in a photo is Levels. When Levels is selected within an image editing program, it brings up a histogram. A histogram is a visual display of the pixels from black to white in an image.
By moving sliders, you can adjust brightness and contrast, improve tonal range and eliminate the "flat" look of many images and bring out more detail. Start by adjusting the black areas (left slider), then the white areas (right slider) and finally, the midtones (middle slider).
Each photo has it's own distinct histogram. When first using the histogram, note where the black and white sliders are positioned. Adjust them so that the black and white sliders are lined up under the data in the histogram. You can also change color balance by selecting an individual color Channel and making similar adjustments.
Adjustments are a matter of personal taste, so experiment until you're happy with the outcome. Always work on a copy of an original. If you make a mistake, you can go back and work from another copy of the original.
Effects of histogram changes on an image
If your image editing software does not have histogram, you can use the brightness and contrast tool, which gives you less control but can be effective.
