programming for posterity

(OR: how to write programs that can be easily maintained in the future)
I was reading today an article that lamented the skills (or rather the lack of them) exhibited by many who today call themselves programmers. The trouble, said the writer of the article is that programming in some common web languages such as PHP means that even untrained people are writing programs - programs that are later found to be hard to maintain and insecure. I agree. Like most everything else in life, programming requires skill and training, and no small measure of planning.