On the NetTuts.com site today there's a set of reminders about some software principles that all developers (PHP or otherwise) should keep in mind when doing their work:

he fundamental things will always apply. If you have an understanding of the underlying ideas of software development, you will quickly adjust to new techniques. In this tutorial, we will discuss three basic principles and mix them with many more. They provide a powerful way of managing the complexity of software. I’ll share some of my personal opinions and thoughts, which, hopefully, will prove useful when it comes to applying them to code and real-world projects.

Their three ideas that should always be in mind during development are:

• DRY - Don't Repeat Yourself
• KISS - Keep It Simple Stupid
• "You Ain't Gonna Need It" (YAGNI?)

For each principle, there's a but of an example showing either some current project that follows the idea or a process that can be used to implement it.