An adequate fuck-ton of coloured pencil how-to references (per request).
Things to remember when utilizing coloured pencils is that you ought to find what works best for you when shading. Some people start with the light colours and shade darker, some vise versa, and some shade with the lightest colour and then go from dark to light. Also recognize that many different colours can compose a single surface (refer to last image of lips). Contrast is a key to making this all work. Focus on manipulating your light to dark shading with a single colour before incorporating many colours.
(P.S. The anatomy in a few of these tutorials is off, but the techniques still apply, I promise.)
[From various sources.]