Ask HN: Best practices for PHP

I've been asked to do a rather large project, which is fine, but I have to use PHP.

My experience with PHP is limited (I'm a Python and .NET-guy), so I don't know the pitfalls there might be.

I read a recently submitted link [1], and thought it was a good place to start, but I was wondering what other best practices or hints/common pitfalls you could mention?

Thanks! :)

[1]: http://www.justincarmony.com/blog/2008/10/25/php-design-biggest-database-oversights/