The NETTUTS website has posted a top ten list of things from the PHP masters out there, a few words of wisdom to live by. Here's the list along with the authors of each:

• Use PHP Only When You Need it - Rasmus Lerdorf
• Use Many Tables With PHP and MYSQL for Scalability - Matt Mullenweg
• Never, ever trust your users - Dave Child
• Invest in PHP Caching - Ben Balbo
• Speed up PHP Development with an IDE, Templates and Snippets - Chad Kieffer
• Make Better Use of PHP's Filter Functions - Joey Sochacki
• Use a PHP Framework - Josh Sharp
• Don't use a PHP Framework - Rasmus Lerdorf
• Use Batch Processing - Jack D. Herrington
• Turn on Error Reporting Immediately - David Cummings

Some of them are conflicting, but that just means that you'll have to do what you've always done - take advice with a grain of salt and ultimately decide what's best for you and your application.