Cartooning is not about drawing it is about telling stories,even when you are drawing a single illustration you are telling a story. Cartooning is about expressing your thoughts. And it is your thoughts expressed beautifully through your cartoon characters that make you different from other average cartoon makers.
1. Do not start with computers. I agree I run the risk of sounding backdated. But here I am not opposing usage of computer altogether, no sane person can do that. But for beginners there is no alternative to using paper and pencil.There are various software that help you so much that you can go ahead even without learning how to draw a smooth line. This kind of over dependency on computers from the very beginning always backfires down the road.
2. Nail the fact in your mind that construction of human, animal, cars and most of the things that that we see around us are complex 3d structures though we draw them on paper which is 2D. So when drawing you must mentally analyze your model in terms of 3d shapes like spheres and boxes and not in terms of 2d shapes like circles and rectangles.Also when you draw something from paper (i.e. 2D), look for and find out the 3d shapes that make up the character.
3. Most of the cartoon drawing or figure drawing tutorials always start with some basic 3d shapes and after a number of steps end up in a complete and beautiful figure. This technique is very effective in learning how we can draw complex figures starting with simple shapes. But what I am going to tell you will make your pace of learning even faster. It is in fact very simple way of using the same tutorial. Just a lot more effective.
2. cartoons drawing course
3. how to sketch
4. here to check this simple tutorial on head drawing