I hate quick&dirty. I think it was my school teacher telling me, while learning GW BASIC and TURBO PASCAL, that when some code looks ugly, the product will so too. After time I've learned exactly that. Technical debt is evil. Rather sooner than later you have to pay back any debt.

It might sound surprising, but the best piece of advice I got were not directly related to programming, but more to the attitude and work ethic. With the years I understood that a strong work ethic and a good attitude are the starting point for solving any technical challenge. Therefore, taken aside all the programming pieces of advice we see anyway repeated in blog posts from time to time, the best things I've been told more than a decade ago are:

• You have the choice: whether you do not do it, or you do it professionally. But if you do it, make sure you are professional.
• when asked for work, you can do it for free, of charge the full price, but never work for cheap. (this one was so useful while I worked as a freelance years ago... spending hours and hours helping people for free on forums, but never doing professional work for cheap)

Later edit to add some time-related context: It might be worth mentioning that I only realized these were really good pieces of advice (at least for my profile) as the years passed. By the time I heard it, it was more like "well, ok, that makes sense" but it's only with the experience that I really get how good they are.

Step away from basic, here's pascal. Step away from pascal here's assembler. step away from asm here's C. Step away from C, here's C++. Face Java. Welcome bash, welcome html, welcome to css, welcome js, welcome to jquery. Best for me was "Welcome to python".

I've learnt a lot from all different frameworks and languages used over the years and the similarities and differences are a worthy addition to any coding class. Never had any useful formal schooling so i can't quote from there.

What has gotten to me lately (in line with remarks from @Sébastien Portebois) is Just F$cking Ship. Providing clarity all the way and more than coding only.