Lips come in all shapes, sizes and colours. In my opinion, the fundamental skills to learn is perspective, lighting and shading... almost anything can look good with great lighting and shading ;)

Perspective is not really an issue in this portrait, so it comes down to lighting and shading. The main principal at work here is just building up the image, working and re-working until you are happy with the final piece. Don’t get discouraged in the initial stages when it looks rough, it only matters what it looks like when you’ve finished :)

There is no ‘right’ or ‘wrong’ way to go about it. Some would say you need to sketch first, or use basic shapes, some don’t. Have a look at other artists techniques and adopt one or adapt to suit yourself.
Start off with basic sketching. If you are referencing a photo or rough sketch,
using a grid reference is a great way to help transfer an image.
Creat a painting layer under the sketch layer. Set the sketch layer to ‘multiply’.
I do most of the painting on one layer, so I pain the skin around the lips to a reasonable level.
As you add colour to the lips, add in shadow which will help keep an eye on proportions and shape.
You can turn off the sketch layer and keep building up light and dark areas.
Start adding the wrinkles and folds. Remember where the light is coming from and add light and dark. If light is coming from left, the light aread will usually be to the right of a wrinkle.
Keep building, no rush. It can take minutes or hours. If it just ain’t working for you,
go have a break, a coffee and come back to it ;)
Now, not all lips have higlights as below, it all depends if the lips are moist, have lipstick etc. If the lips are dry, we would probably skip the highlights and carry on with shadows.
What we’re looking for is contrast between light and dark as this helps with giving the appearance of depth in a painting or drawing.
Finished Painting