You did exactly as I did in my first trials making hair
... To draw hair you should layer it down to create the texture.As a first approach is good what you did, but it looks like a drawing.
You could use it as a deeper exercise: I would work over it by smudging the graphite and giving a general tone. Then add more tones by adding layers (coloring) slightly the hair following shapes and direction of the hair. Then you erase the highlights, and re-layer the dark, and repeat...smudge,color,highlights, darks... you'll see it looks more realistic.