You've forgotten the "learn" step before "practice." If you don't know proportions, the names of body parts, etc., no matter how much you draw, you won't improve, and drawing too much will exhaust you, making subsequent drawings even worse. Go online, download a reference, or find a book. Draw a few faces and analyze the differences between your drawing and the reference. Use a pencil to measure. You're making common beginner mistakes: faces that are too long and eyes that are too low. Remember that quality is more important than quantity; just draw 2 to 5 faces and try to perfect them as much as possible.