Thank you for your analysis Jorge, as always very helpful. You pointed my weakness, I always wonder if on white of the face can be white of the paper that is what I often do. On other hand I often think in that case it is the same colour as the surrounding and if it is all right? Should I try just light graphite instead of white? Another thing is transitional border between medium and dark is it OK to make it sharp?

Yes, I noticed that when the image is small then it is easy to see which areas are too dark because the whole face looks very weird and that helps me to correct some areas.
My unsuccessful drawings do not discourage me but motivate to try again until I am satisfied. I definitely continue to practicing and would be good to have your expertise on my side, as you always do :)