vetyr answered:

Thank you! There’s one thing about drawing portraits that I don’t think I’ve ever touched on, and it’s the technique of constraining features. Basically, it becomes easier and more intuitive to rotate the face in 3D space once your mind grasps exactly where the features are located and, furthermore, where they can’t be located.

I use a weird double trapezoid shape that I’ve depicted below in red to keep track of facial feature placement every single time I draw a face. It follows the top of the eyebrows, touches the corner of the eye, traces down to the corner of the lips, and finally ends at the bottom of the lips.

The shape of the constraint will change depending on the person’s features, and it works for every angle of the head. For me it really internalized where each part of the face was, as well as where it started and ended. It kinda helps moderate your drawings; i.e., you’ll stop drawing features that are wildly misplaced or off-sized. I don’t literally draw this shape out every time I draw a face, but I see it in my mind’s eye 100% of the time.

If you’re still learning proportions, a good exercise is to grab pictures of people and trace this shape over them (either digitally or with a marker or something) to get an idea of what realistic constraints looks like. Then go back to studying faces, and constantly check your drawing by tracing along the eyebrows and down to the bottom of the lips to make sure that things aren’t off (e.g., the constraint isn’t terribly asymmetric). It takes a while to get used to, but it might help you get a good feel for portraiture.

There’s one other unrelated thing I like to do with faces, and if you’ve seen a lot of my pics you’ve already picked up on it. If you kinda add some shading to the area on the cheek just below the eye and down to the nose, I think it adds a decent amount of depth to a face. Don’t go overboard of course but there’s another little tip that could be of use.