A good attempt, but if you want to get better from faces what you want to do is start with drawing skulls and studying facial muscles.
You have to walk before you can run, and that same principle applies to stylization! If you don't have the fundamentals down, it can be the difference between getting a Motorcity or getting a Johnny Test.
As you're drawing those skulls, try to work mostly from real-life pictures and recreate them as closely as you can. People give a lot of guff to tracing, but as long as you don't try to pass it off as your own work it can be a really solid way to get your hands used to the movements and better understand the contours and shapes you need to focus on!
Some skull references to work from, to start you off:
https://www.google.com/search?q=real+skull&espv=2&biw=1600&bih=731&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiylcTGkanNAhUDx2MKHR41C2YQ_AUIBigB
