I don’t think that anyone can easily describe you what to do. Thats something you have to learn by time. Learn how to model a head, then how to stylize that head. How to model cartoon face. Prepare a good references of your face front, side and 45° degree shots. I dont know if you are a beginner or higher level modeler but dont expect to model a perfect self cartoon portrait without modeling a hundred heads for practice. I would recomend to:
- Learn topology and how to model head
- learn how to sculpt head (may be a better workflow for you and retopology after)
- learn differences between realism and cartoon stylized
- learn how to use references
You will find plenty of tutorials for any of this.