- https://github.com/thoughtbot/guides - This is not actually only ruby guide, but overall guide for engineers, I personally don't agree with everything there, but still good reference.
Best Practices - SOLID
- https://robots.thoughtbot.com/back-to-basics-solid - a good start of solid principles
Best Practices - Design Patterns
- http://designpatternsinruby.com/ - Nice book giving solid details of almost all Gang of four design patterns
- https://github.com/nslocum/design-patterns-in-ruby - this github repo has references to the book design patterns in ruby it has some examples inside the folders