Install the pre-requisites
$ sudo apt-get install build-essential openssl libreadline6 libreadline6-dev curl git-core zlib1g zlib1g-dev libssl-dev libyaml-dev libsqlite3-0 libsqlite3-dev sqlite3 libxml2-dev libxslt-dev autoconf libc6-dev ncurses-dev automake libtool bison subversion
Download and install Ruby
$ wget http://cache.ruby-lang.org/pub/ruby/2.0/ruby-2.0.0-p247.tar.gz
$ tar -xvzf ruby-2.0.0-p247.tar.gz
$ cd ruby-2.0.0-p247
$ ./configure
$ make
$ make install
Check the installation
$ ruby -v
ruby 2.0.0p247 (2013-06-27 revision 41674) [i686-linux]
Install Rails
$ sudo gem install rails