Some useful techniques in debugging PHP are mentioned below

• Article: http://dev.piwik.org/trac/wiki/HowToSetupDevelopmentEnvironmentWindows
• Firefox addon – Firephp
• PHP Extension – Xdebug
• Using var_dump()

  <?php
  	var_dump(__FILE__, __LINE__, $_REQUEST);
  ?>
  

• phpEd
• Zend Studio (5.5) with Zend Platform
• Using, print_r and echo

  echo "<pre>";print_r();echo "</pre>";