Tutorial - Curves on Girls by *Ai-Bee on deviantART. Reaaaal good tut on different body types. In her deviant there is also a lot of links to others tutorials for men and women body types. If you draw characters, go see this.
Guías de dibujo: Anatomía y movimientos del cuerpo
By placing lines at various distances from one another, the image gets more structure and gives the illusion of a body. A variation in width gives more dimension to the image and illustrates a sense of realism.