Which (eyes, nose, hair) gives you the most trouble?
Focus on the "under-plane" (the nostrils and septum) rather than the bridge. Secrets to Drawing Realistic Faces
Drawing a realistic face is less about "talent" and more about training your eyes to see shapes rather than symbols. Most beginners fail because they draw what they think an eye looks like, rather than what is actually there. Master the Proportions Which (eyes, nose, hair) gives you the most trouble
Use a mechanical pencil or a "stippling" motion for subtle skin texture. Secrets to Drawing Realistic Faces