Draw the basic outlines of the lips first. remember that the bottom lip is usually thicker. Also, females have fuller lips than males.
Shade in the lips quickly using a fast back-and-forth motion with the pencil. The upper lip should be shaded in darker.
Blend the pencil smoothly , erasing the smudges outside of the lines. Go over the lines and make the line between the lips dark. Fill in the lip corners darker as well.
Blend thoroughly. Use the eraser to add a highlight in the upper and lower lip, blend to smooth it into the lip. Add more definition with shading if needed. The corners/edges are usually darker. Done!