Portrait Drawing Feedback/Critique

Hello! I've been practicing drawing faces/heads for the past 3 weeks and would like some feedback on what areas I can focus on. I do a 30 minute class session daily focused on expressions. Attached are some of my most recent drawings sorted from least to most recent. Thank you very much!

https://imgur.com/a/cj1tu8V

Keep practicing and it will all come along ;)
More construction lines will help you improve quickly (if you learn them and keep working)
This video is one of the most helpful I find :

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Hello, Learning Artist, and welcome to Line of Action, I'm Polyvios Animations, and how are you?

Say, Learning, you must be definitely on the right track on understanding the basic head construction of your head portraits. Great job, I say, so please keep up, but the head forces all look and seem a bit too somewhat rigid to me. How would you like to lighten up your lines therefore be even far more decisive in your graphic lines with 28 minutes of 2 minute head warmups?

Because, if you warm up your lighter lines and lightest shapes, then your understanding and control will be developed into being the least stiffest and the most dynamic, energetic, and furthermore, liveliest in communicating your expressiveness. For most info, look into a copy of Andrew Loomis' Drawing The Head and Hands. Good luck, and may you find these encouraging and helpful and informational.

The video also shows well the weaknesses of the method. Individual features disappear and the end result looks like a prototype. The shapes of the nose and mouth are wrong. The shape, size and direction of the eyes are different from the model.

Thank you for providing a direction to move forward with. I'll try with the excercisese you recommended, thank you!