This is a bit outside my comfort zone, but I thought I'd have a go. If you don't think it looks like Kate Middleton, at least it's a tutorial on drawing pretty, young women!
Drawing portraits is very difficult if you don't know the person. Many of the drawings you see on Youtube are straight reproductions of photographs. That's the easy way to do it and they are very slick and look right because they look like the photos you know already.
I think you learn a lot more about drawing by trying to understand the way a face is put together and then trying to draw from what you have learned. You will then want to practice the drawing many times to get it right and in doing so you will learn a lot about how faces are put together.
Find out more about me and my books at my website http://www.shoorayner.com/. Look me up on Amazon or in your local bookstore. I've illustrated over 200 books in my time! Enjoy!