Here is a guide to install the Nautilus Elementary Ambiance GTK theme by simplygreat.
First you need to install Nautilus Elementary, open a terminal window and copy+paste the following lines:
sudo add-apt-repository ppa:am-monkeyd/nautilus-elementary-ppa
sudo apt-get update && sudo apt-get dist-upgrade
When installed you need to restart nautlius, to do this copy+paste the following line in your terminal window:
nautilus -q
Now you can install the Elementary Ambiance theme
sudo add-apt-repository ppa:victored/ambiance-evolution
sudo apt-get update
When done run a system update using the update manager (press Alt+F2 and type: update-manager) to install 2 new packages, light themes and a new icon theme called ubuntu-faenza-darkest. When the updates are installed you need to restart nautilus again.
To use the theme click with your right mouse button on your desktop, select Change Desktop Background and click on the Theme tab. Now you can select the Ambiance Evolution theme and when selected click on the Close button and enjoy the Ambiance Evolution theme.