If you struggle with coloring faces and hair you might want to get some great insight from "Coloring Faces & Hair with Copic Markers" by Marianne Walker. It really gives you some great fundamentals, PLUS images to scan and color. This book gives very clear instructions, giving you a step by step in the coloring process.
Here is something I colored from the book.
The author wrote it so it starts simple and then progresses to more complex like the braids I did above. In this over 50 page book, it also has a coloring chart for skin, hair and eyes so you can document your favorite blends.
For those of you wanting to get more practice in, or just getting started this is the book for you.