[animeomarguy]

Basically, you need three things:
1)Proportion-Which has been repeated a couple times.
2)Shading-Shading your drawings create a sense of 3D, which makes artwork pop-up right before your very eyes.
3)Detail-Everyone can draw a face, but adding detail will bring your art to life. Adding simple touches, like scars, dimples, moles, and so forth will greatly improve the art.

And I guess that would the all...Those are the ones that came to mind =P