I don't have my original list from 3~4 years, a job, and a move across the country ago but here is the gist:

• symfony.com/doc/current/best_pract... (symfony specific)
• php-fig.org/psr/
• Always test your code, a mix of automated and manual
  • Especially in web a unit test doesn't tell you the website looks awful
• Keep functions/methods simple (doing as few things as possible)
• Use/create libraries/services when code will need to be reused.
  • But keep them simple, you don't want a million flags just so you can cram everything into one function
• And whatever else you might do write comments/document your code.
  • People need to be able to understand what you are accomplishing (including yourself 6 months from now)

Now not all of these may apply to you, such as Symfony, but I think for the most part these are universal.