In this one I didn't do any drawing on top of it, all I did - literally the only thing I did - was select the jaw and mouth and move them up a bit. There was a lot of excess space between the mouth and the bottom of the jaw and it looked a bit like the face didn't belong.
I also moved the mouth closer to the nose, but that was just me getting carried away. It wasn't really necessary.
I got a bit carried away here too. I meant to only draw over the outline of the face and I wound up doing the hair too. Notice that I did not touch any of the facial features, just the face shape. It was really sharp in the cheeks and the chin didn't quite line up with the rest of the face. It was also just a tad bit long. You can barely see it but I also drew a slight dotted outline of the bald head and the hairline. Doing this can help you make sure that the hair is placed properly and that the bangs are starting at the hairline and not above it.
I would really love to see what kind of guidelines you use when drawing faces, if you use any. I know sometimes people don't think to use them, especially in the beginning, but they can be really helpful. If we see how you are starting your drawings it gives us a better idea of your process and helps us to help you.
So yeah, just be careful where you place the features and maybe observe people around you to see how real faces are structured.