Try to draw sketch of a full human body. To make the full figure you can start with the basic shapes like round or oval. Then try to put in complete details. Practice to get the general proportions right. You can exaggerate the size of the head. This allows you to get facial expressions that can be easily seen. In drawing cartoons you can also exaggerate the facial as well as body proportions a bit to make the cartoon look funny. Though overdoing it will not have a good impact. Initially try to make the body proportions right and after lot of practicing exaggerate the proportions for comical effect. Try to draw figures of all types of people – fat, lean and average.