I would start with the quote:
"if the only tool you have is a
hammer, you treat everything like a
nail". (Abraham Maslow)
The most important principle, IMO, is to know many different programing paradigms, languages and inform yourself well about the tools on your disposal. Any problem can be solved in almost any language you choose, be it full blown mainstream language with its huge default library or small specialized language like AutoHotKey. The first job of programmer is to determine what to use according to the specification of the problem. Some concepts provide better approach to topic, whatever your main goal may be - sophistication, obfuscation, performance, portability, maintance, small code size ...
Otherwise you will finish like some of programmers who desperately try to do something in a 1 language they specialized, while the problem could be trivial to solve in different programming context.
This advice goes along with todays tendency for multi-language projects (take web applications for example, which may involve several languages in single application, like C#, JS, CSS, XPath, SQL, XML, HMTL, RegExp.... and even different programming paradigms (for instance, C# introduced recently some concepts from functional programming paradigms, lambdas).
So, the basic thing is constant learning, forever :)
