Need tips on Drawing Portraits

Hello! I'm struggling to draw portraits with expressions. Straight faces are not a problem anymore. Any tips or references?

Thank you for asking this question. It has inspired me to research to understand facial muscles and how they move. There are 43 muscles in the human face. That's what I got from the how stuff works.com

I found this video recently about facial expressions; it was very helpful!

And it also has a second part, I didn't watch it but it goes into further detail:

In terms of references, Noah & Rachel Bradley have a nice set of expression references available:

https://reference.pictures/expressions/

Hope these resources help a bit!