From 2002, J. Scott Johnson's Software Engineering Practices for Large-Scale PHP Projects presentation (viewable with Internet Explorer only):

"Aspects of Large Scale Projects:

• Version control
• Design notes
• Code reviews
• Knowledge capture
• Bug tracking
• Test plans
• Event Logging Throughout The Code
• Error Handling Throughout The Code
• Dynamic Error Alerting (to administrators)
• Redundancy
• 0 Data Loss
• Translation
• Human Understandable Error Messages
• Separate the HTML from your code
• Separate the text from your code
• Documentation"