Great job on the character portrait here. Tings to practice would be the figure mannequin and perspective. The torso perspective especially. For the hair you kind of have the right idea, you just need to create one silhouette for the hair. (Darkest value) then draw interesting ribbon shapes using the freehand selection tool and filling them with your medium and highlight values. Hoping this helps you with some ideas and gives you some things to practice.
Thanks

