Design for how you live
The single principle beneath all four levers: a small home should be shaped to one household's actual life, not furnished from the inherited large-home template (bedroom set here, dining set there, sofa facing TV). Every lever is a way of throwing off that template and starting from real life.
The whole course, in one sentence
Subtract asks what you actually use; Layer what your rooms must actually do; Extend how the space could actually feel; Storage where your real things actually live. A well-designed 500 sq ft can feel more right than a thoughtless 1500. The method fits your life into your space, exactly.