I have been a tech writer, and I would say something similar, that you need to know two things to write well: audience and purpose. The road becomes a lot clearer after that. Rules on writing fill whole books, but most writing would improve tenfold if writers remembered audience and purpose.

How do you fumble something so obvious? Selfishness. The poorest writing I've ever come across I have to assume that the writer is not writing primarily for the reader. He's writing for his boss ("My boss told me I have to write documentation. Once I get this done, he'll be off my back."), for his company ("I have to cover every possible shenanigan in this license or my company might get sued"), for his paycheck ("I'm going to pour on euphemisms like maple syrup so the reader can't help but be hynotized into buying our product"), or for his ego ("I'm going to use really big words, fashionable memes, and a chummy style to get people to think I'm smart.").

All of the other sins are microscopic compared to the writing from selfish motive. Most of the other rules fall into place if you remember just this, love thy neighbor as thyself.