On the Smashing Magazine site Glen Stasberry has posted a few tips to help improve your PHP development practices.

Because of PHP's huge popularity, it has become almost impossible for Web developers not to have at least a working knowledge of PHP. This tutorial is aimed at people who are just past the beginning stages of learning PHP and are ready to roll up their sleeves and get their hands dirty with the language. Listed below are 10 excellent techniques that PHP developers should learn and use every time they program. These tips will speed up proficiency and make the code much more responsive, cleaner and more optimized for performance.

Suggestions include using a SQL injection cheat sheet, "shortcutting" the else in your conditionals, don't use regular expressions if you don't have to, using ternary operators and using memcached. You can see the full list here.