Redirect Users After Login by Role in WordPress

You can redirect users who log into your WordPress site to different URLs based on their role.

function redirect_user_on_role()
{
	global $current_user;
   	get_currentuserinfo();
 	if ($current_user->user_level == 0)
 	{
       	wp_redirect( home_url() ); exit;
 	}
 	else if ($current_user->user_level > 1)
 	{
       	 wp_redirect( home_url() ); exit;
 	}
  	else if ($current_user->user_level >8)
 	{
		wp_redirect( home_url() ); exit;
 	}
 	else
 	{
     		$redirect_to = 'http://google.com/';
       	return $redirect_to;
 	}
}
add_action('admin_init','redirect_user_on_role');

For more security best practices, see Hardening WordPress Security.