Best place to start is by sketching a circle for the head. it doesn't have to be perfect and remember to sketch lightly. Then you move on to the torso, an oval makes up the shoulders.
 
You then build up the rest of the body using rectangles for the arms and legs.
These shapes are just what your going to work on top of not what your final character will look like.
From looking at this you get the basic idea of how a character is constructed.

For more detail in the arms you can use ovals and circles.

 


When drawing female characters to make the shapes of the arms and legs less square..of course this also depends on what kind of outfit you plan to have them wearing

 
The same shapes can be used for smaller characters. These type of characters can be fun to draw as having the body structure accurate is not important.
 

All work shown here is copyrighted to Emma Goodman, unless otherwise stated.