Charcoal Portrait Sketch vs. Reference Material

Here's a side-by-side comparison of my recent charcoal portrait sketch of Esme' and my reference photo. 

With the images cropped similarly and lined up next to each other, its easy to see how much I've exaggerated the size and contrast of the eyes, and taken some licence with the value and contrast range. I've also unintentionally made the nose a bit too narrow.

Exaggerating the eyes was intentional to some extent, although I think I took it too far in this case. I can get away with it in this loose sketch, but in a painting this would add a cartoon-ish, stylized feel to the portrait. This isn't necessarily a bad thing, but it wouldn't have been my intention. 

It's important to be aware that everyone, no matter their skill or experience level, will tend to exaggerate expressive facial features like eyes and mouths because they are psychologically so important, and draw so much of our attention. IF you are aware of this tendency, then you can work to mitigate for it by careful observation and measurement to double check your proportions.