Hobby Hint
I use a permutation of the "traditional" mix as introduced in Shep Paine's book: burnt sienna + gold ochre + white. To this I add a bit of raw umber, and an extremely small amount of prussian blue. By "extremely small" I mean just a toothpick-tip's worth. I've found the addition of blue to tone down the inherent reddish tone inherent to burnt sienna. I've also heard that adding a bit of green has the same effect, but I haven't tried this out yet. For an undercoat, I've taken to using Vallejo medium flesh with a very thin layer of Testor's dullcote lacquer; this in an effort from keeping the Vallejo acrylic from lifting from the piece (something I've had problems with at times).
For shadows, I've just added burnt umber to the base mix and applied it wet-on-wet. For highlights, titanium white is added to the base mix and applied wet-on-wet as well. I've never had much luck with colors such as naples yellow red or jaune brillant for the highlights - maybe this is due to my heavy-handedness with the painting technique.
In fact, that's always been a problem of mine when painting fleshtones - knowing when to stop. After applying and blending in highlights and shadows, I just let the piece dry over night. After drying, I hate to admit it but I block in the shadows and highlights again so as to accentuate them a bit more. For highlights, though, I've found myself applying about three consecutively lighter tones in layers, much like it's done by acrylic painters.