I choose to make my self portrait. If you want place reference image on background layer, and start drawing on new layer. Use Pen tool to create head’s contour and with Convert point tool create vector shape. Right click and choose make selection, fill selection with color.

Use same technique to create selections like in previous step to make shadows on head. When you have selection choose dodge/burn tool to create shadows. (use 0% for hardness)

Now with pen tool create line. Stroke path by right click, ‘Stroke path…”. Repeat that for other lines.

Place shadows on t-shirt and draw mouth and eye-brows.

You have to use pen tool again to draw border of hair precisely. Create eyes and color it, than place some shines in eyes. 

Fill selection of hair and place shine and shadows on it. Fill background and that is all.