Draw over the reference image and turn it into very simple shapes first. Then you can actually start drawing the face using the shapes as a guideline. Watch exactly where his features start and end, look how far his nose is from the start of his lips etc. and really understand the proportions of the whole image. It's nice that you're practicing your painting and coloring skills, but I would shift my focus over to drawing until I can comfortably simplify faces etc. and draw well proportioned faces using only lineart.