It's easy to install.
You can either use one click install:
Go to http://software.opensuse.org/package/numix-icon-theme and choose your version and install it.
Or better, open a terminal and execute as super user:
1. Add the repository:
zypper ar http://download.opensuse.org/repositories/home:/paolorotolo:/numix/openSUSE_13.1/ numix
2. Install the icons and theme.
zypper in numix-gtk-theme numix-icon-theme-circle
Open GNOME-TWEAK-TOOL and change everything:
It'll be better if you enable GLOBAL DARK THEME, so it'll be the same as the numix window theme.
Check out, how nautilus look like