Below are examples that show what lip-lines, nostril and mouth corner details are and how they look.
Lip Lines - subtle lines added to the lips vertically to give texture.
Nostril - adding paint or blushing to the inside of the nostrils. May work for only certain sculpts.
Mouth corners - adding definition to the corners of the mouth to help with expression or detail. They can be added in a range of intensity from light to dark.