Sketching manga style face from imagination…

Hello! I have just watched a YouTube video regarding facial proportions (dividing the face into four equal parts to locate the mouth, nose and eyes etc). I am trying to learn manga style art and I did a five minute quick sketch of a young female and male side by side. I usually copy from a photo but this time I tried to draw from imagination.

Any suggestions or constructive criticism will be welcome. I want to master drawing faces first and then move onto drawing bodies and clothing.