To add to @echo_jk great feedback, I think you could apply the same thing she mentionned to the hair. Finding the volumes in the hair can be a bit difficult so I like to start by simplifying them into simple shapes, almost like ribbons, so it's easier to get a sense of the volume. And then I gradually add details as I go along.
Speaking of the details, I find that keeping hair details more towards the extremeties of the hair (like the roots and the tips) and the places where hair get tighter together makes the hair look better and less busy than if you detail the hair everywhere. It might just be my personnal preference though.
With all of that said, here's a quick and rough example of how I approach this. I changed and simplify her haircut a bit just for this example, but you can obviously do much more detailed and intricate hair styles than this with the same approach.
I hope that helps and I feel like there's a lot of cool stuff you could do with this. So keep it up 
