Hey bycristian123, To begin with, you need to make sure your drawing is solid first before you worry too much about rendering. As far as the rendering is concerned, I would use graphite instead of charcoal, it's much easier to handle. When it comes to adding shadows and rendering, you have to remember that it all has to do with the light. The light direction in particular has a lot to do with how the shadows look. It also creates the separation between light and dark. When light hits the body it helps describe the form and the casting of shadows across other forms. Also, the farther the light travels, the weaker it gets, so everything is a little darker the farther away from the light. I did a quick sketch to show you what I mean, I hope it helps :)