This is a little esoteric relative to the world of quick-changes that most of our code in WordPress is. But if you’re writing PHP or JavaScript in much depth, you’ve probably heard of the SOLID principles. These are rules of good software development made by Robert C. Martin. Code that follows the principles is generally thought to be of higher quality than that which does not.
Dan North, for whom I have a great deal of respect (because a lot of people I respect seem to respect him) thought it would be fun to riff on this idea with his own principles properties. And I found it useful and informative reading. If you’ve never heard of SOLID, maybe start there. But if you’ve read at least a little on SOLID, I really think you should give this CUPID article a read 