Separate Code from Layout
Don't mix "PHP":http://www.php.net code and HTML in your scripts. There are several templating systems for _PHP_, one of which is the "Pear":http://pear.php.net package "HTML_Template_IT":http://pear.php.net/package/HTML_Template_IT. It is easy to use and allows the complete separation of HTML and code in your scripts, therewith making both the _PHP_ code and the HTML easier to maintain.