ok i haave some tips.
For airbrush:
1. First before you start click the + that's by brush dynamics.
2. uncheck pressure- opacity | check pressure-hardness | Check velocity-opacity, hardness and rate
3. leave all the other stuff unchecked and put it on the fuzzy brush.
that should make your shading a bit smoother, for extra clean look blur it a bit.
also i like the shape of the eyes but idk if that thing below it is suppose to be a mouth or like a mouth piece. but gj ^_^