My advice is to try more contrast and colours. Take a close look at skin, there are all sorts of colours in it, depending on where the light is coming from, oranges, pinks, purpley and reddy colours. Try really exaggerating these to start, and then gradually toning them down until they look natural. Also, make your shadows and highlights really stand out! This will help to give your drawing the feel of being a real object, with form and mass. Try working from a mirror or photo reference, but instead of drawing wht you expect the shapes to look like, really LOOK at it, try to understand WHY the shadows are here, highlights there. Touching an actual face can help, feel up your own face, poke around to find where the bones are, where the slopes are, what moves where when you smile or frown. If you can find a willing volunteer, feel their face as they make different expressions and watch how the shadows move. This sounds kind of awkward, but I find it's one of the most helpful things when I'm stuck with a painting. Also, it seems you've chosen really grey colours for your shadows and highlights. This makes your lady look a bit dead, I would try some more saturated colours to give her a little more life.

This is pretty good :)
I would have liked to see a bit more contrast in the skin tones, but I think you did a good job.