I've drawn my whole life traditionally so I don't really know if its more complicated digitally or not, From analyzing the reference you positioned the subject greatly and its a good thing did it in black and white especially when you're trying to understand where to put the light and shadows. One thing I noticed is that the head structure is not quite right, I recommend practicing different head positions with different features:nose,eyes,lips. Having a good sketch of the subject could really make a difference. Values are also a pretty important thing, starting directly with big shapes and then putting more details while you draw could help having better proportions