Some pointers on making your Ruby parameter defaults self-documenting.
Learn a concise way to treat a module as an object in Ruby.
Learn how to break a dependency on a pervasive mixin.
Shortcuts to reading and writing files in Ruby.
Learn how to present a natural interface to client code, while hiding implementation architecture details.
Understand when and how to use Ruby's array combination methods.
Stop thinking of variables as boxes.
Grouping data by various properties is easy in Ruby, and there are more uses for it than you might think...
Write intention-revealing loops with Ruby's Enumerable#cycle method.