Still Life is an icon set which aims to provide realistic, easy, and non-distractive icons.
It is mostly adhering to the GNOME Human Interface Guidelines and is still quite young and incomplete. This is a work in progress, much more things still to come.
Go to Desktop - Preferences - Theme
Click on Install Theme button and chose the icon archive.
Then go to Theme Details and go to Icons Tab and chose from the list the icon theme.