Uh, well first of all I use Paint Tool SAI as programme. And then... it's not very difficult, for example if you have to colour the hair, just use a light colour as base. Then, create a new layer and select the 'clipping group', or something alike xD Use a darker colour and shade the hair, then use another colour, even darker to shade again. To make lights, in most of the cases I add another layer, I set it into 'overlay' and I choose white as colour. I hope this helps a little c: