Different users swear by a number of different methods to use to improve color. Many of these techniques are complicated or heavily theoretical and most won't necessarily show more improvement in an image than a simple, controlled Levels correction.
The idea of Levels correction is to redistribute and essentially stretch the information recorded in the image to make the most of it. This, in turn, broadens image contrast and adjust color casts. As a result, the one simple correction can make an image both more dynamic in tone and color, as well as make the image look more color-realistic, or color correct. Levels corrections are often most effectively made by cropping the tonal range cutting off histogram tails. Cropping is done by moving the black and white sliders toward the center of the graph.
[NOTE: Tail refers to a histogram graph area where image information is present and measurable on the histogram, but appears as a thin line and may be image noise rather than necessary image detail.]
Corrections can be adjusted and improved beyond the Levels correction, but understanding this simple technique opens the door to learning to use more complex tools (such as curves). Although several other tools will often be necessary to fine-tune your color corrections, Levels can often solve many basic problems quickly. Color Balance, Variations, Eyedroppers, and Selective changes are other tools that will be used here to refine color results.