Learn to think about thinking. At the basis of every program lies a human being's mental model. Creating a program which accurately reflects a shared mental model is crucial to building habitable and maintainable systems.
East-oriented code. Learn how to better understand encapsulation and create code which enforces that the right objects have the right responsibilities.
Data, Context, and Interaction (DCI). Discover ways to flatten your object structure and create highly cohesive groups of objects that keep related things together, right where you need them.