Can you elaborate, for the non-linguists? His prescription seems sensible:
i. Never use a metaphor, simile or other figure of speech which you are used to seeing in print.
ii. Never use a long word where a short one will do.
iii. If it is possible to cut a word out, always cut it out.
iv. Never use the passive where you can use the active.
v. Never use a foreign phrase, a scientific word or a jargon word if you can think of an everyday English equivalent.
vi. Break any of these rules sooner than say anything outright barbarous.
... but I'm well aware of how sensible an asinine prescription can seem to a layperson.
For example, "the passive" is rarely defined in a coherent way, or matches the actual definition of "passive voice". Worse, though, is that it is very bad advice. What are called passive senses are tools to correctly place emphasis which, done well, aids clarity.
Often a long word captures a nuance the short version can't. Its presence, by itself, calls the careful reader's attention to the distinction between it and the shorter word it displaced, without belaboring it.
Metaphors, similes, and figures of speech are the furniture of language. Most words, standing alone, embody one. Orwell certainly did not obey this stricture, or he would have been mute.
A word that could have been cut, but wasn't, calls attention to the choice made not to cut it, inviting curiosity why it wasn't, which you may then answer.
Foreign, technical, and jargon words tell the reader about your context. Substituting a word unfamiliar in that context generates confusion, and questions about what distinction you are trying to make by avoiding the usual word. Sometimes you are, in fact, making such a distinction.
Careful readers learn to recognize when writers are making their choices judiciously, and draw extra meaning from them.
So, better advice would tell you to put each such choice to work on the hard job of communicating.
This is not just personal distaste. Linguists who know the facts find it intolerable.