Many amateur artists expect to be Botticelli within an hour of picking up a pencil. But the truth is, most aspiring sketchers will spend more time erasing a mouth that's out of alignment than stacking up completed drawings. The lips are recognized as one of the trickiest parts of the face to draw convincingly. The softness, the many creases, the varied shapes — getting this across in grayscale can seem an insurmountable obstacle, but, like anything else, it just takes a lot of practice.
Most people know the lips belong about two-thirds of the way down the face. What they may not realize is that the angle of the jaw and the bottom lip correspond closely. Additionally, the inner corners of the iris (the colored part of the eye) align with the outer corners of a closed mouth. Some new artists also rush to make the central mouth line — the aperture — a straight line when it should, in fact, be curved.
When drawing generic male lips, the aperture is less defined and will require less pressure on the pencil. When drawing female lips, the aperture stands out more - it will be the darkest part of the mouth.
The Cupid's bow is one of the central parts of the mouth, which the eye is naturally drawn to. This is the center of the top lip that dips down. The shape and depth of this aspect of the face can significantly impact the finished product. Practice drawing this gently curving line on scrap paper before you sketch it into your work.
Very lightly, sketch in the creased area between the upper lips and nose. Though the first instinct might be to draw two vertical, slightly curving lines, take care to make this area subtle, not sharp and eye-catching. Take a look at your own face in the mirror. You'll notice this area is mostly identified by shadow, not lines.
A bottom lip naturally displays creases, and an artist can exaggerate these vertical lines on a closed mouth. Each lip has around twenty creases, though many are very faint and shallow and not easily visible. To capture a realistic-looking mouth, add a few creases.
On most faces, the top lip and the philtrum are shadowed a bit by the nose. As a result, the top lip requires a bit more shading than the bottom. Remember that even the tiniest gradient will have a big impact on your work, so keep the darkened sections still quite light. You can always enhance the shadow, but removing it can create unwanted smudges.
Much like the nose shades the upper lip, the space between the lower lip and the chin is often in slight shadow from the lower lip. Realistic-looking portraits often feature a shadow below the lips, the length of which ranges from a sliver to a thin crescent, depending on the fullness of the lower lip (a thicker lip casts a longer shadow).
For the darker parts of the lips, you can always go back over your sketched-out piece using charcoal or a darker pencil to the shadowed areas. Many artists will use a 4B pencil for this task; this firmness delivers a natural finish without blackening out too many details.
At the center of the lips, focus on emphasizing the natural shadows for effect. This will depend, of course, on where the light is coming from in you piece, but in most cases, the bottom lip will catch the light more than the top one. Some artists conduct this part in layers, and will come back to add further shapes, like triangles and squares of light, later on.
Finally, the easiest way for an artist to contrast light reflections is by rubbing out some of the parts they have shaded in. This will smudge away the dense pencil lines, drawing attention to areas like the center of the lower lip, showing where the light bounces off the model's face.