Draw the boundary of the upper lip like this, making it a little heart-shaped.
Draw a curved line for the bottom lip.
Separate them with a line curved downward at the centre.
Fill in the upper one with a red pen.
Fill in the lower lip lightly except for the bubble. This will give a glossy look.
Shade with a red colour pencil. Aaaand, you're done!
- Red pen
- Red colour pencil