Not
very many 40k races have skin showing, except for the Imperial Guard and
the Orks, but I will show how I paint skin, and also cover the area of
painting eyes, just incase you might need a hand.
I start
painting skin with a base
colour of Bronzed Flesh over the top of a white undercoat. I will use
this Pit Fighter as an example.

When
the base colour has dried, I then apply a coat of Flesh Wash (what else
should it be used for?). I make sure that the wash settles in the 'valleys'
of the muscles, and in the folds of the skin, like the eye area, around
the nose, mouth and ears. I also make sure that the wash sits alongside
other objects that lay right next to the skin, such as the shoulder straps,
and chainmail gloves. Here is what my wash coat ends up looking like.

Once
the wash has dried completely, I then go back to the Bronzed Flesh and
paint the first highlight. In the picture below you can see that I have
left the wash in the appropriate places. So, basically, any area that is
raised, gets repainted. You can see on the face how I have picked out the
forehead, eyebrows, cheeks, ears, nose and chin line.

It's
at this stage that I can start to see the image come alive. The last step
is one more highlight. For this I use Elf Flesh, for it's lighter tone,
rather than mixing Skull White into Bronzed Flesh. I have again picked
out the same places on the model, but with less area, such as the point
of the nose, the highest point on the cheeks and the lips. I have also
put some Armour Wash (for it's black tone) in the mouth. As the pigment
is not as strong as Black Wash, I can still see where the teeth are without
having to strain my eyes.

As
the flesh is now finished I can concentrate on the teeth and eyes. As this
is a Pit Fighter, I decided to give him metal teeth. So I used Chainmail
Silver to pick them out. But for normal teeth you might like to use Bleached
Bone or Skull White. As for the eyes, you really need a steady hand a fine
pointed brush. Starting with Chaos Black, I fill the eyeball area, trying
not to get any on the top and bottom eyelids.

After
the Chaos Black has dried, I then apply Skull White to the center of the
black area. I prefer to have the white touching the bottom eyelid, and
this in turn leaves a black area above. This will help reduce the effect
of the model looking like it is staring, rather than being angry.

The
the last and final trick is to put in the pupils. Using Chaos Black again,
I apply the paint so that the top and bottom of the dot are touching the
top and bottom of the eye whites. Again this helps to stop the staring
appearance as you can see below.

So
all in all, he doesn't look too bad. All that needs to be done now is to
cleanup the surrounding areas where I have got flesh colours on parts that
I didn't want (you guessed it, I'm not perfect). But I really should start
drinking less coffee.