Hair can be such a tricky part of your drawing and so I took a look at Youtube to see if there are any useful videos. Of course I was not disappointed, there are tons. I've shared a couple here which I thought were particularly helpful, see what you think and please let me know if you find any other good ones.
Firstly here's a video from the very talented Stan Prokopenko
Secondly a video by another huge talent Wei Ho, I hope you find these useful :)