"If you intend to make a living at drawing, by all means learn it [the rules of perspective] now, and do not have them bothering you and your work for the rest of your life."
Good sources to reference for perspective.
Creative Perspective for Artists and Illustrators by Ernest W. Watson
How to Draw Comics the Marvel Way by John Buscema
Perspective for Artists by Rex Vicat Cole
Marshall Vandruff's Perspective series of videos