Hey! Nice images <3
While I am not at all an expert; from what I can tell you are using small brushes TOO early in your painting process. As for resources, I suggest watching Istebrak, Scyra (?) , etc. and performing form studies.
In the second image, you values go way too dark and way too light. By converting your image into grayscale, You highlights seem to be what we call "no man's land." It is almost impossible for skin to be THAT bright because you are using almost PURE whites. The entire painting itself looks very blurred and I am forced to look at the tip of the nose. What I suggest to fix that is to create harder edges and shade radially.
GREEN suggests area where line dependency shows.
To solve this I suggest painting broader strokes (blocking in) and only use smaller strokes when RENDERING.
RED is where the PUREST whites are. It is way too bright and should not be used in the name of science.
Overall; I suggest to performing grayscale form or photo studies. Sorry if I wasn't too helpful here. 
