It's pretty easy to know that interior holes should come from an initial block that then gets cut. The part that takes polygon modelers a bit to get used to is also treating ends of shapes in that same way - outside areas and ends of things that are not regular shapes (like not planar or not 4 sided) should usually come from cuts in the same way that inner holes come from cuts too.

It can help if you kind of thing of it as more of a real life construction process like where you are working with some board or piece of material and you're slicing chunks off of that stock material to form the final shape.

- Michael