Ok, maybe I can revive this board, by actually helping people. (I should create some kind of art course.)
You seem to be practicing quite a bit. That's good.
What's you're goal in art? Depending on your answer I'll be able to give you better tips and hints.
>[...] I also got told that I should learn the proportions of the face [...]
Learning the proportions of the face is alright, if you have no fucking clue how the human face looks, because you've never actually consciously paid attention to the proportions.
But that only gets you so far, because it's restricted to the front, back, top and both side views.
It doesn't teach you the three dimensional forms of the head and face. (You would be suprised how much the skull shows through, when it comes to drawing a face.)
I would recommend you to study the skull.
After that take a look at the muscles of the face and neck.
So, you make a hyper realistic value copy of a skull from a few different angles. (Don't add color. It's just distracting.)
Just copy a reference image. (This one is a really good excercise. You might not believe it, but through working on a single skull for a long time, you really start to pay attention to the forms. The image of the skull will be burned into your brain. And you'll be able to remember little details you would've never noticed in the first place.)
After that you should be able to construct skulls from any angle. (Or at least from the most important angles.)
Now I would more or less learn a bit about the facial musculuture. Just enough to get an idea about how it might affect the face.
Then take a few pictures of really beautiful people. Or the kind of faces you would like to draw. Maybe you want to draw ugly jew noses or so. Dunno what the kids nowadays are into.
Study the proportions of those faces.
What I mean is, try to find patterns and rythms in the face.
Take a look at the picture and develop your own method of constructing that face.
Make sure you can create something similar and appealing using your newly developed method. Don't look at the picture.
If you can't construct it with your current method, find new rythms and relation lines.
I would post some of my studies, but my laptop doesn't recognize my SD card... D:<
Ok, now to the value thing.
My development was as follows:
Drawing very high contrast paintings, which look totally off.
Me: "Ok, I need to learn to be more subtle about values."
Draws very low contrast paiting, with very subtle value shifts. (Learned how to control value and be very subtle in the way I blend them.)
Me: "Ok, it still doesn't look realistic, it's somehow missing that realismTM.
Then I realized that the realism comes from the contrast. It makes images pop and feel like they're jumping out of the canvas. That's why TVs always brag with their value range and how much contrast they have and how that contrast makes everything look 10x more real.
Now I draw painting, which look decent.
Me: "Ok, that's pretty good, but other artists stuff looks even better. How do they do it?"
This is when I read a forum entry from a chinese artist, who explained how peoples images are overall too bright, which makes the images look less impactfull.
His technique was to make everything a bit darker, because the white of the canvas or the white of the screen will never be as bright as the sun or a real light source.
So by making everything else a bit darker, that makes the light appear even more real.
Me: "Ok, sweet I can paint. TOP KEK"
 I would like to show you the studies I did a few years ago, but I basically lost all of my work, when I changed from Window to GNU+Linux and from Photoshop to Krita. Also I alwaysdeleted all of my drawing once they were done, because I was all about that grind. If I cherished a painting or drawing that would mean, that I couldn't replicate it. "FUCK THAT! I know how to draw that shit. I'll redraw that thing ten times again, and make it look even better."
That was stupid. Saving these drawings is great for tracking progress and making you feel good.