Switching from drawing what you see to constructive drawing.

[Punk-A-Cat]

If you haven't seen it already, http://drawabox.com and the cntrl-paint (not sure on the spelling of that one, but google should find it?) both have bits on form and construction. I started out the same way, and it was a struggle to figure out the form in objects, both those sites, and funny enough anatomy drawing using the bean shape - proko.com helped with it.

I'm still no where near good at it, but it helped.