I have a large jar of Tamiya NATO Green that I use as the base color; I have some black and a GW Yellow that I use as mixers.
Start by mixing 1:1 Green+Black; paint this into the crevices and stirations of the muscles. Mix this color up in a couple coats to a pure Green, by which time you should have covered the whole figure (skin anyway.) Start adding Yellow to the Green and thin this color down so it mixes smoothly. Paint onto the highlights like cheekbones, biceps, shoulders, knees. Keep mixing this color up to almost a pure yellow. Use the (thinned!) pure yellow to hit the very highest of highlights; the edge of the cheekbones, the nose, the point of the chin, the specular highlight of the bicep etc.
If you want to do this fast, just take 3 colors (1:1 Green:Black, Pure Green, 1:1 Green:Yellow) and do the whole thing in three coats with no blending.