This is the quickest/easiest way I can see for someone running Mac OSx to get up and running with Ruby on Rails assuming they are starting with a blank slate.
Just dumping it here for future reference;
curl -L https://get.rvm.io | bash source "/Users/your-username/.rvm/scripts/rvm" rvm get stable rvm reload rvm install 2.0.0 (this might take some time and you may need to enter your password a couple of times) gem install rails
Now you are ready to call
rails new my_awesome_app