Well one this i notice right off the bat is that you need more contrast with your colors, also the skin on the first one looks like it's just gradient shaded, try to to use your colors more for highlighting certain areas more than just making darker and darker shadows to show depth, Both peices could do with a bit of antialiasing as well. Also although dithering looks good in some places as a way to show depth i wouldnt use it as a style of highlighting areas such as in the hair. All in all it's better than most first post stuff i see on here, you seem to have the anatomy down pretty good. just a few fixes here and there would really spruce these up.