Right well, what are you painting?
Any pictures? What colour scheme are you going for? Will the skull be painted in a generic colour scheme, how technical does the freehand need to be? Will there be any OSL on it, is there just the skull, or other stuff on it.
What type of skull are you trying to paint, is it a human skull, ork skull, animal skull, alien skull?
Have you tried to do any research by yourself, have you been on google or yahoo and searched for images, or sites about bone structure which you can use and look at for reference?
I might sound a bit narky but people can\'t really help until you give us something to go on. Explain what you are trying to do fully, and what you have already tried to do.
And give pictures of any attempts you have already tried etc...