I went to an art school in brooklyn & learned 3d design as part of a formal spatial program. The big insight that was beat into us is to start by simply symbolizing an object - squint at it until the rest blurs away - and then gauge/adjust/repeat the relationships between the pieces you're left with. Persist until it's second nature and it'll be powerful magic for a designer in any field. Abstraction can be rather useful, in a conference room or a startup.

here's some background:

http://www.rowenafund.org/about/rrk_about_rowena.html

http://boxesandarrows.com/view/foundations-of