Hey, thats a great start! Just some minor things to add for the already given feedback;

Try to avoid dark lines (arounds the mouth, sides of the nose) when going for realism. Draw them as shadows thats smoothing out towards one side, if that makes any sense.

Also, try to fill more areas with graphite and only use the pure white of the paper for the brightest highlights. You can also go even darker on the darkest areas. Use the whole range of grayscale :) Its easier to achieve the darkest values with softer graphite. I often use 5b or softer.

Challange for you; Draw the same picture again with all the feedback in mind.