First when you go to do a study of anything new... review what you are familiar with. Last year, you drew lots of faces. Now the tricky thing is to draw your own. Yikes! So it is key not to not forget to use guidelines and measurements that you already know.
Beyond the measurements remember how value effects the form and visual planes on face.
Second, remember geometry... your face is made up of visual planes. Squint your eyes and you will see the planes come together like puzzle pieces.
These planes reflect how light hits the face.
SQUINT YOUR EYES AND FIND THE PLANES!
Third, never forget the importance of gesture! It is your greatest storytelling messaging device. Drawing faces is a lot more than geometry especially when you are drawing your own. Messaging is very important. That's why Rembrandt said gesture is...
He knew a thing or two about drawing portraits.
The gesture in the hair offers great framing and contrast to the smooth sculptural quality of the face.
Play with framing and contrast so that you set up the most important elements you are trying to give emphasis to.
Play with lighting! Light gives drama, adds intensity. The true ooohs and ahhhs come from lighting not color, Value makes color sing in tune! Get it right and everything will fall into place.
Remember you should have at least 3 facial studies or more!