Anyway I wanted to talk about construction a bit.
Personally when I can't think of anything to draw, I basically just practice the basics such as construction and the ability to change the shape. I believe that the more I draw these shapes and practice changing them, the more likely I can draw them better and with better control (As you can see some of them ain't as solid as I'd like them to be).
You see when I was still at school, I had to make a choose between two different subjects (There were others but these were the two I wanted to try) which were Art and Graphics. Now my dad is pretty skilled at drawing goldie oldies so I felt he could teach me the art side of things and so I went with Graphics.
Unfortunately my dad didn't teach me much about Art and for years I felt that Graphics was the wrong choice for me and that I missed out on Art but now I'm starting to understand it because of the strong influence of construction, perpective and materials within the subject.
So if I was to recommend a subject to cartoonist that are still at a young age, I'd say Graphic is a good start.