Convert an existing static website to a responsive website

I need to convert an existing website to responsive. It is a custom website developed in Ruby on Rails framework (version 1.1.6). I would like to convert just the public views of the front-office of the website at this moment. I am determined to manage the conversion in a practical way, adapting the web design to the easiest way to make it responsive. You should be familiar with Ruby on Rails and web design to accomplish it. A way to test the responsive design in some views will be appreciated it.