There're three categories of themes: Gtk themes (that control how the window contents is themed), Window title bar themes (known as xfwm4 themes in Xfce/Xubuntu) and icon themes.
How to install themes
Depending on the category of theme you're installing, extract the theme to one of the following locations:
- Gtk and xfwm4 themes:
- Icon themes:
Hint: If you're running Xfce 4.10 you can drag-and-drop the
*.tar.gz file containing the theme in the dialog for changing the theme.