When I was in third grade, I remember coming in to class one day, and the teacher had drawn three examples of simple 3D drawings on the board. From the second I saw them, I knew it was going to be a fun day! Those three basic examples were a cube, a cylinder, and a pyramid:
Back then it was just pencil and paper, which in some respects is easier than Flash, but not as precise and clean. There are some areas where pencil and paper just don't make the grade. For example, it's not so easy to flood fill like you would with the Paint Bucket Tool in Flash, and it's also a lot harder to use gradients well with a pencil. So Flash it is!
These 3D shapes are very simple to draw, but a tip before you start working through these examples is to have the Snap to Objects option selected (make sure View > Snap to Objects is checked).