My personal top three should be something like:
- Be humble. Everyone makes mistakes. Every programmer writes bad code once in a while. Swearing at the code and blaming others is unhealthy. Avoiding this kind of behavior is very hard but must be done (I'm still struggling with it).
- KISS > DRY. Very often, keeping things simple is better than avoiding repetition. Always write code for other people to read. Keep methods small and chose meaningful names. Try to write code that matches the verbal explanation you would give if someone would ask you "what does this code do?".
- Keep related code close. It's VERY painful to maintain code that is spread across multiple files, in multiple directories. I'm not saying one should mumble the code all in one place. But mind the separation of stuff in your project. Different functionalities might be on different places, but one functionality should preferably be in one place, be it a file or a directory.