Anime/manga seems to be as good as anything else. The lines will shape it up, that's the important. Work each field with one colour and thin it where you want highlights, then go over it with a darker version of the same colour in the shadows.
A bit like Michelangelo does in this painting:
Another effective approach is to limit the colours to one or two colours + black for the shadows. It normally gives a cool look and is easier to control.
Like William Blake:
