Most important basic philosophy “simple vs. easy”: Rails Conf 2012 Keynote: Simplicity Matters by Rich Hickey (Slides)
You probably know this already and in Ruby not all of it is done “explicitly” but it’s important to have these principles in mind when getting to know the following architecture concepts.
STUPID: Singleton, Tight Coupling, Untestability, Premature Optimization, Indescriptive Naming, Duplication
SOLID: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion