Great start, I can tell by the studies that you seem to be serious about improving. If you're intent on learning more realistic faces I would suggest taking photographs from wherever (your own, stock photos, etc) and tracing over the features. Not to publish of course, but juustt as an exercise to help you better understand how proportions /really/ work rather how you -think- they work. Doing this a couple times helped me understand eye sizes, the distance between the eyes (i always draw them too far apart, ack), etc etc. Once you feel like you've somewhat grasped it, do some more studies and then solidify what you've learned with freehanded stuff from imagination. Just a thought! Keep it up and good luck.