The easy way
Make sure you're in your home directory, then copy and paste this into your terminal:
curl -L http://github.com/expectedbehavior/common-files/raw/master/.common_files/install.sh | bash
Check out the install script if you like. It's pretty close to the lines below.
The hard way
The common files are meant to be installed into your home directory, but Git is a little reluctant to put itself right into an existing directory. Install by checking out to a directory and then copying into your home directory:
git clone git://github.com/expectedbehavior/common-files.git cp -fr common-files/* . cp -fr common-files/.??* . rm -fr common-files/
This works by default on most *nix systems, but on OS X you'll need to change the mapping of the page up and page down keys. In terminal, change page down to '\033[6~' and page up to '\033[5~'.