Draw a simple horizontal guideline for the mouth placement
Mark the center line of the face
Sketch the upper lip with a light curved line
Sketch the lower lip with a softer, smaller curve
Keep the mouth small and simple for a manga style
Adjust the curve for the expression you want
Add a slight dip in the middle for a neutral mouth
Make the corners turn up for a smile
Make the corners turn down for sadness or anger
Open the mouth by drawing a second line below the upper lip
Add a small shape inside for the tongue if needed
Keep the line weight clean and minimal
Erase construction lines after finishing
Refine the shape to match the character’s age and style