Like Will said, it would be hard to distill that experience into an email... Maybe a course or two...! Any takers?
There are some good books out there on refactoring and writing portable code that I found instrumental, but like Derek said, practice and experience are the best teachers. To that end, I recommend trying practice problems: Koans, Coding Dojos, DailyHacker, Project Euler. All these are great ways to practice your craft, and the best way to hone it is to practice.
As for learning what you don't know, look for opportunities to work with people that know more than you do, no matter how much or for how long, and always look for opportunities to learn from whatever assignment you're given.
Finally, many thanks for the glowing compliments, Will. I know my tenure was brief, but I'm glad to hear I had an impact. Cue Indian with single tear on my mark, Mr Crusher. :D
David @ OrlandoPHP.org