Face proportion
All teen or adult human faces fall into nearly the same proportion. Our faces are all nearly exactly the same as far as placement of our features and how far they are from each other. Our ability to recognize different people and emotions is a remarkable tool of judging the very slight changes in our features shape. As artists we can use that continuity to create generic faces that seem real, and we can distort the placement of the features to create fun strange faces. This page will help you with both images and videos.
Drawing exact portraits from photos...
These portraits should be of someone you like enough to honor with your time. It takes me between 7 and 10 hours to do these right, so pick someone you want to spend that much time on. I suggest you draw a family member, maybe find a photo of your grandparent when they were your age. Follow the comparative measurement process to accurately draw their form. Note that as a line drawing the likeness will be good, but it will only truly resemble the person you are drawing when you shade the values, so I like to define the major value shapes with a light contour to help me shade the correct areas. Also note that much of the face will be the subtle values like the light value of the top of a box, so start soft and build the values carefully.