Practice human head ("stylized")

Good morning, Once Filo, and welcome aboard. How are you doing this morning!

You know, I think that your head gestures are on the righter track, but I feel you're getting the great range of expressions and emotions of the exterior positives and interior negatives in your faces and expressions. Please keep pushing yourself as farther as you can go, and then push farthest.

I'm not getting enough of that creative caricature and artistic distortion in your expressions. Please would you like to try out 1 hour of 30 second scribble faces? (120 scribble sketches)

As a result, your signature style of drawing facial relationships will get to become the least blandest and the most animated, cartooniest, and humorous as the legacied Daumier, or maybe even more so. For most inspiration of gesture drawing, look up "Honore Daumier gesture sketches." Good luck to you, and let's hope these have been the nicest, the most helpful and encouraging to you.

The proportions are great!

You could try to focus on drawing different perspectives (of the head and/or the anatomy) and see if you "understand" and can apply easily the results to get a good sense of proportion.

Ultimately, if you feel there's something off, you can take a photo of your sketch, digitalize and send it to your PC. Open an image editor (photoshop, gimp, etc) and compare your sketch with the reference to see analyze those details.