I could use some tips on tanning skin.. Everything I do just does not seem to add the right color..

I found by accident that if I copy the blue channel as a layer and set the blend mode to luminosity it simulates a tan (at least in the couple I tried this on).

I also found that by converting to CMYK and increasing the Cyan, you might get closer. Keep in mind that the Magenta/Yellow have to be reasonably equal percentages. As a starting point only, try slightly more yellow than magenta and Cyan about 1/5 to 1/3 magenta, then try gradually increasing the Cyan. This is assuming Caucasian coloring.
This may give you somewhat different results to Doug's, but it seems that playing with the Cyan/Blue (luminosity) might get you close.

Cheers
Dave

using the channel mixer and reducing the green channel a tad and the blue more than the green.. Methods sound similar I will give them a try they sound more promising though..