Technique: Working with Levels
Basic color correction can show dramatic improvement with the smart use of Levels. Here, the idea is to redistribute the information available in the image to broaden contrast and adjust color casts. Although several other tools will probably be necessary to fine-tune your corrections, the Levels can solve most of the basic problems quickly. Color Balance, Variations, Eyedropper checking, and Selective Color changes will take care of the bulk of the rest of the correction.