Perspective applies to all objects in the same way, whether they're simple or complex. So mastering perspective for primitives will help you tremendously when drawing more complex objects.
Knowing how to construct an object with the help of vanishing point projections is not what this is about, though. It's about getting an intuitive understanding of how perspective works.
So drop your ruler and start practicing drawing primitives from all kinds of perspectives. The point is to learn how to do it without using references, but you should compare your drawings to real objects or use guidelines in the beginning to make sure that they're accurate.