It's difficult to get flesh to look right, but I think I've found a good approach. I used to start with Citadel Tallarn Flesh on a white or black undercoat. However, while this provided good coverage, I found that the pigment of the Tallarn Flesh was a little heavy - probably because it's from Citadel's Foundation range. I still use it on my ogres, but for humans I now do the following: base coat Army Painter Matt White, then a thinned coat of Privateer Press Ryan Flesh, covered in a liberal wash of Citadel Ogryn Flesh. It looks a little like this:
This is very good for a quick first stage and it gets a reasonable contrast between the highlighted and shaded areas on the face and hands. Once the clothing is done, I'll return to do another wash in the deepest areas, then several layers of highlighting with the Ryan Flesh mixed with Skull White.