You've got a great start Valerio! I'm liking the line variety you've got going especially in the second one. Similar to what Arthur said, I'd say practice some head anatomy more. Andrew Loomis is a great place to start as he breaks down the head in a clear and simplified way. Also check out using the Reilly Method to help in construction and getting the face (this will work for the figure as well) to tie together from side to side. The little drawing I included is a trace over of your second drawing using a combination of the Loomis head and the Reilly Method. One thing when studying Fechin, is to be watchful of how he designs the face, and breaks the rules. What I mean by rule breaking is that you'll see him purposefully* distort certain features, or the thirds of the face, bend the center line etc.

I like the shadows on the second one! All though I think you could do some work on the anatomy of the head, drawing the default skull from diferent angles would help a lot. The cheekbone of the first one for example seems to be pushed too deep and it's pointy. Keep the great work!