Ok first off this is the first I have ever done, so please if you dont
understand the way I explain things then let me know and I will try to
be clearer

This is how I work.
These are the things that you will need:

The paper that I am using for this picture is very smooth bristol
board, your paper needs to be quite heavy and smooth because of the
blending you will be doing.
First off find a photo that you like this one that I have chosen is my daughters friends daughter, she is such a cutie pie.
here she is :

Sketch out a copy of your chosen photo on paper. If you think you wont
be able to get a likeness then print off a copy of your chosen photo
and trace it onto your paper with a pale brown coloured pencil. I use a
window to do this, simply put the copy behind your good paper and rest
it on the window and very lightly trace around the outlines only.
I look at the picture and decide where the shadows are and with a light
brown (sorry not using a well know brand using Steadler Ergosoft chalky
leaded pencils). Very very lightly colour the darker parts of the face
(you need to be really light here, no pressure just barely touching the
surface of the paper, if you press too hard you will leave indents in
the paper and this you will never get out later). Once you have done
this take a tissue and gently in circular movements blend this very
soft pencil.
here is an example:

I usually repeat this step with just a light brown several times again very lightly.
Now
I want to add a little colour and build up the depth of the contours of
her face. I have used a little purple and light blue for the shadows, a
little orange red and rose for the cheeks, nose and forhead area and a
little yellow that will bring out the highlights later.
Here is a pic with the colours that I have used so far:

The face is really lots and lots of very thin layers of colour gently
blended with a tissue, you need to repeat over and over again until you
have the desired depth.
I have now decided that I need to colour
her eye's, again its the same process of very light pencil strokes,
take alot of time over this because they need to look like your
subject, keep your pencil leads sharp for this, and try to keep a small
bit of white free for the light refelection.

Once I am happy with they eye, I begin to lift some of the blended
colour with my kneadable rubber, you just have to dab at the paper in
the areas you want to be light: