300 isn't a DC comic. It has its own independent creation and doesn't fall under the DC Comics universe. The story and characters are distinct from DC's offerings.
Well, to sculpt comic figures, you need to have a clear idea of the character's features and proportions. First, make a rough sketch of the figure, then start shaping it with clay or whatever medium you prefer. Pay attention to the small details like facial expressions and clothing folds to make it look realistic.
Vampirella wasn't a DC comic. She has her own independent comic series and background separate from DC's universe. DC has its own array of characters and storylines that don't include Vampirella.