The saying "less is often more" applies to the colors you use when mixing skin tones. Using fewer colors, or a limited palette, means you learn how they work together faster, and makes it easier to mix the same colors again and again. Which colors you use depends on the darkest tone you require. Limit yourself to two or three colors plus white at a time, then experiment with different combinations of colors until you find what works best for you.
In the figure study shown here, I've used two colors plus white. Burnt sienna and yellow ochre mixed with one another and with white give a wide range of skin tones. What they don't give is a very dark tone. For that I would add either a dark brown or dark blue (most likely burnt umber or Prussian blue). Even with this extra color, I would still be using only four.
I didn't mix the colors on a palette first, but painted without a palette, blending the colors straight on the paper as I painted. I was using Atelier Interactive Acrylics which you can keep workable by spraying with water. The burnt sienna is a semi-transparent color which used "full strength" is a warm, rich red-brown (as you can see in the hair). Mixing it with white shifts it into an opaque color. A very small amount shifts titanium white into pale flesh tones.