Search these forums. You will find many threads with professional artists saying that there is no formula for realistic skin. I can say however that you need good colors to make good skin tones.
I would say a palette with at least white, yellow ochre, transparent oxide red, burnt umber, viridian, and lamp black would be good to have when working with skin. That is of course, for relatively " normal" lighting situations.
"A drawing is not necessarily academic because it is thorough, but only because it is dead. Neither is a drawing necessarily academic because it is done in what is called a conventional style, any more than it is good because it is done in an unconventional style. The test is whether it has life and conveys genuine feeling."- Harold Speed [[Sketchbook]]