Natalie Portman Portrait

Hi Deviouslylinked,
Overall, you did a pretty good job on this portrait. Kudos for tackling one of the most iconic actors around and doing a convincing job!

For me, the things you may want to work on to improve are:
-Form: although the overall proportions are right, the face suffers a few issues, mainly in terms of form or volume. The nose feels a bit flat on the face and the mouth and chin are a bit too much to the viewer's left.
To improve this, try to start with a very light and simple sketch and place the different elements of the subject, using basic forms (spheres, cones, cubes, cylinders and pyramids) Play with that for a while before getting into the details and shading : first, you need the structure to look right.

-Shading: You did an excellent job on the hair and a good job on the face! That's a great thing but it means you are taking the attention away from what should be the focus of your drawing. At the moment, I think the face lacks highlights that would make it pop out more.
To improve this, keep in mind that the viewer's eye will be drawn to the areas of highest contrast. It means that you want the higher contrast to be around the important features of the face: usually the eyes-nose-mouth triangle.

In the same vein of idea, try and "frame" the face with areas of very dark shadow in the hair around the edges of the face.
Finally, you can also frame the whole portrait in an area of pure white. This process is called alternation and is good to make a picture more interesting: the idea is to have a dark area standing out from a light area. You can repeat the process, for example : a light face standing out from dark hair, standing out from a light background.

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I hope this will help you improve. You are already up to a good start and, with a bit of work, could achieve great results!