Look for generalities (like the top lip is thinner than the bottom lip) and uniqueness (when lips are shaped differently, like top larger than bottom). When you learn to study your subject closely, you will get them right. Just like my guidelines, imagine a line between the mouth’s corners, then everything will be clear. TIP: When you draw the mouth’s corners, do not draw them sharp-pointed like an arrow! It’s an area where the top and bottom lips intersect, so make sure they have a fair amount of volume. The lips with red lines gives that 3D appearance. It helps with the contours of the lip and understanding the shading. ANOTHER TIP: For the profile view, the top lip normally protrudes more than the bottom lip or as much as it. The 3 lips in the lower right-hand corner are sketches of unusually positioned lips, puckering, lick, biting on lower lip. Crazy, fun poses like this make your drawings priceless!