Using levels in Photoshop can be effective, but if you move the left or right hand sliders you’re almost guaranteed to lose information. The reason is that even if you don’t see any detail in the highlights it’s still likely that there is some detail there. A much safer way of changing the highlights and shadows is to use an RGB curves adjustment. After shifting the overall curve, you can go into the individual color curves to fine-tune the adjustment.

If you’re using Photoshop, I’ve occasionally found the Color Balance tool to be helpful.

As for getting a particular gradient to a certain hue, the Channel Mixer is a powerful tool. Since the primary color of skin is red, you can adjust the hue of the skin tones by adding/subtracting green and blue to/from the red channel. Green carries much more luminosity information than blue or red, so if you add green to the red channel you’ll get brighter skin tones. It takes practice, and isn’t appropriate for all situations, but it’s very useful.