Aqui está uma coleção de artigos interessantes com as melhores práticas para Ruby on Rails.

http://www.antoniocangiano.com/articles/2007/02/10/top-10-ruby-on-rails-performance-tips

http://glu.ttono.us/articles/2006/02/06/rails-best-practices-tips-and-tricks

http://wiki.rubyonrails.org/rails/pages/RailsBestPractices