Top ten tips - http://blog.sudobits.com/2011/05/01/top-10-tips-and-tricks-for-ubuntu-11-04/
(OR)
Open gconf-editor (hit ALT+F2 and enter ‘gconf-editor’) and go to apps -> Metacity -> General and select button layout field and change the default value to -
menu:minimize,maximize,close
(OR)
gconftool-2 --set /apps/metacity/general/button_layout --type string menu:minimize,maximize,close
(OR)
Open gconf-editor (hit ALT+F2 and enter ‘gconf-editor’) and go to apps -> Metacity -> General and select button layout field and change the default value to -
menu:minimize,maximize,close
(OR)
gconftool-2 --set /apps/metacity/general/button_layout --type string menu:minimize,maximize,close