Base Coat
These steps should be completed with an airbrush as it's much easier to get the shadows and highlights correct.
Step 1
Cover the face completely with a reddish flesh color. This could be replaced with a deep purple for older skin. Other colors can be used for different effects, even using green for orcs.
Step 2
Spray Kislev Flesh directly from above, then pull down from the front to a 45 degree angle. This leaves the darker shade in the shadowed areas but applies the base color for the skin.
Step 3
Spray the Flayed One Flesh directly from above, then pull down again from the front at a much smaller angle. This applies the brightest highlights to the face.
Step 4
Apply a gloss varnish. This will make applying the followup glazing steps much easier and will result in a smoother result. You can also black out all other details other than the skin to help prevent distraction.
Contouring
Step 1
Glaze the entire head with a reddish tone very thinly. Apply a second layer if needed to change the hue more. This step is to darken the skin slightly, allowing the skin to be highlighted back up to the previous step 3 highlight without having to go with a lighter color.
Step 2
Apply a medium brown as a semi-opaque wash very finely into the recessed areas to tint the shadows. Focus under the eyes, around the ears, cheeks and along the hairline. Keep the face held towards you to help ensure the shadows are placed correctly. Once complete repeat this step with a darker brown where the darkest areas would be.
Step 3
Apply the base coat step 3 color as a first highlight. Apply it to the nose first to check that it isn't too stark against the glazed skin. If it is you will need to find a darker tone to highlight, but as the nose will be the brightest you won't have just made a mistake.
Step 4
As a final highlight apply tiny dots to the highest points such as the nose and the eyebrows.