What is the key to good writing?

According to George Orwell there are six rules that all writers should observe. The first five can be linked back to Fowler's Dictionary of Modern English Usage first published in 1926:
  1. Never use a metaphor, simile or other figure of speech which you are used to seeing in print.
  2. Never use a long word where a short one will do.
  3. If it is possible to cut a word out, always cut it out.
  4. Never use the passive where you can use the active.
  5. Never use a foreign phrase, a scientific word or a jargon word if you can think of an everyday English equivalent.
The sixth rule is a little more controversial:

6. Break any of these rules sooner than say anything outright barbarous.

Orwell's definition of 'barbarous' is brilliantly displayed in 1984 and is centred on the idea that political thought and language control was a sinister tool and  by-product of totalitarianism.

Why I Write (Penguin Great Ideas)