I see what you mean. Here are some of the things I notice that would help you out. You shaded some of the details with shadow (I know, I am already speaking nonsense) instead of slightly different skin tone. Also, the plastic look comes from the fact that you used one set color for the skin, instead of adjusting the color slightly where the light hits (example, have her skin at the brighter points fade a slight bit to yellow instead of straight to white). Skin is more that just a color darkened and lightened according to light, but has an assortment of colors (like white skin is a bit of pink, yellow, tan, white, and sometimes grey; black skin is a bit of brown, khaki [on the greenish side of it], tan, black, and red). But you don't have to go all crazy with it, unless you are trying to create a very realistic texture look; however these color so show a bit more in light or in the dark depending on the angle of lighting and type of skin and the condition it is in. And unlike skin, plastic is a consistent color and very smooth, skin isn't consistent and even the smoothest of skin has things that will alter the appearance (like small pores and fine hair,or no hair at all). The trick is figuring out how what changes the color of the skin and how- can be just the shape of the body or it is a different pigment type (some people instead of going slightly yellow in the light, you would go more towards a soft pink).
It gets much more complicated than this, but this should give you a bit of understanding and a good starting point.
Oh, and the perspective if off, her head looks like it is turned slightly sideways, yet her face is diretly forward facing you.
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