It's kind of hard to give you advice based on the pic at this point. From what I can see, it looks pretty good. I would work on blending the shading in, and then adding a layer of darks for the darker shadows on the skin. And I don't know if you want to modify the skin color to make it warmer, because the tone is kind of gray. I depends on how you blend in al the skin tones, I guess. Block in the hair and whatever else you are going to have in the picture. It will give a better sense of what you are aiming for, and people can actually give you advice about those parts. But yes, it's looking pretty good so far. I would suggest you think about that mouth comment ivorybyrd made in post 3.
I don't know if this will help at all, but here's a digital coloring tutorial that I like on deviantArt:
here.