There are several ways to do this but as I, like you am a
beginner I'm going to use the method that works best for me.
There are also some quick tips which you can find in
The head & face.
tutorial but below is a more detailed approach.
The first thing you need to do is to
decide the shape of your mouth and lightly sketch the outline. Don't
worry about shaping the lips yet, all you are looking for is the
overall look of the mouth. The other important thing to do is make
sure you have a sharp pencil.
Copyright © 2009
ACHD

Copyright © 2009 ACHD
Once you have the basic shape of the mouth you can decide how you
want the lips to look and lightly draw them in.
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Now you have the basic outline of the mouth and lips you can
start to shape the lips. I always find that if I use the basic
principle of ovals, circles and triangles I can shape a pretty
convincing mouth. The size of your shapes will define the look of
your mouth so make sure you use the right size shapes. The larger
the shapes the fuller the lips.

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ACHD
As you can see. Once you have added your shapes the mouth begins
to take on a whole new more convincing look which you can work on to
perfect its final shape.

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ACHD
Once you have perfected the shape of the mouth and lips you can
add a little detail and bring your mouth to life. As this is only a
beginners guide all I will say is try to pay attention to where the
light is coming from and always remember to shade or colour the lips
in sweeping lines to the shape of the lips as they are always three
dimensional.

Mouths are not easy so don't give up. Keep experimenting with
different shapes and sizes and you will soon be drawing convincing
mouths.