I don’t see any big or obvious mistakes here. You have improved a lot. 
Maybe the bottom lid could be painted slightly shorter on the outer side, and the white of the eye could be less rectangular there.
Depending on your style and how scary the character is meant to look, the mouth could maybe be painted a bit bigger? If it stays small it is more on the cute side.
Aside from that my only advice is that you could try something more complicated now that you got the basics down. Like adding a background and/or different light setting, coloured light or more than one light source. You could also learn about using gradients (for shadowing for example). 
As you asked about colour specifically, here is some examples from this site where you can see how gradients can improve colouring - especially make your art look more vivid (may not be needed for a vampire, but everything else :D)