Prerequisites

This tutorial assumes that you are starting with a fresh Ubuntu 12.04 LTS installation (it was done with a clean-slate VM). Most likely, your machine will already have many of these items already installed.

Install ROS Hydro

Full instructions are here. Here is the super-condensed version for Ubuntu 12.04 LTS:

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu precise main" > /etc/apt/sources.list.d/ros-latest.list'
wget http://packages.ros.org/ros.key -O - | sudo apt-key add -
sudo apt-get update
sudo apt-get install ros-hydro-desktop-full
sudo rosdep init
rosdep update
echo "source /opt/ros/hydro/setup.bash" >> ~/.bashrc
source ~/.bashrc
sudo apt-get install python-rosinstall