Lips, like the nose, can be divided into sections. The ends are inverts of each other and the middle dips on the upper lips and rises on the lower lip. Of course, there are variations to the lips and can be thin and even curveless. Male lips tend to be on the thinner side and females, curvy.
As with the front view, quarter and side views of the lips can be divided into sections. For quarter views, the middle of the lip is now near all bunched up at one area and tapers to a point at the end of the lips. There is still the dips and the rise on the lips - just closer together. For side views, all you have to remember is that the lips come together to form a point - a sideways "v".
Now on to drawing simplified lips...
The left image shows three simplified versions of lips at profile. Notice how the head corresponds with the lips: simple lip = simple profile, realistic lips = realistic profile. Of course, there is also the middle ground. Some more examples below at quarter view with ranges from simple to realistic.
If you still have some trouble drawing lips without the
three lines to help you as in the previous page, all you
really need is the middle line. Whether the lips is on repose
or is moving, as long as you have the center line to guide
you, you should be fine. Don't forget to erase it though!