If eyes are the soul of a portrait then lips are the ones to express the mood. The expression on the lips control almost the entire contour of the face.
So here is the lovely lips giving a big smile and showing off the sharp nose and chubby cheeks.
1. Monochrome colour outline
2. Applying colours to define the light and the shadow parts, to get the basic contours of the face right.
3. Refining the colour tones, by enhancing cooler colours (shades of blues and purples) in the shadows and warmer colours (shades of yellow, red, white) on well lit parts.
4. Highlighting the areas which have maximum contrast, like the bright spots on the nose, under the nose, lips (makes it more realistic). Softening the edges of the lips which are in the shadow part.