How to change the default action of the index controller zend

I have just created a new Zend project. I want to use the setDefaultAction to change the default action of the Index controller to any other action of the Index controller. I know that I need to code something like :

$front = Zend_Controller_Front::getInstance();
$front->setDefaultAction("about");

but in what function I need to code this? Do I need to do something else?