1. Draw a line to indicate where the lower part of the upper lip and the upper part of the lower lip meets. This line would not really be a straight line. The middle of the line goes a bit deeper, while the sides close to that middle should be given a slight upward curve, such that resembles u.
2. Draw an outline of the upper part of the upper lip. Let it be a bit higher than the line previously drawn and let it maintain the same position towards the middle part.
3. Now draw the lower part of the mouth, which is the lower lip. Sketch it in such a way that it looks like a shallow u. Let it extend from the right end to the left end of the above line.
4. Draw uneven vertical lines on your lips to serve as the creases. The vertical lines would be more noticeable on the lower lip than the upper one.
5. Add shade to the lip, such as painting it. Let the shade be obvious on a part, maybe the lower lip, to indicate shadow.