The keynote [of a pretentious style] is the elimination of simple verbs. Instead of being a single word, such as break, stop, spoil, mend, kill, a verb becomes a phrase, made up of a noun or adjective tacked on to some general-purpose verb such as prove, serve, form, play, render. In addition, the passive voice is wherever possible used in preference to the active, and noun constructions are used instead of gerunds (by examination of instead of by examining). The range of verbs is further cut down by means of the -ize and de-formations, and the banal statements are given an appearance of profundity by means of the not un-formation.
The message seems clear: use verbs and the active voice wherever possible. However, in this very passage Orwell himself does not practice what he preaches. He uses phrases like "the elimination of", "in preference to", and "an appearance of" (instead of "eliminate", "prefer", and "appear"); he also uses the passive voice several times in this short passage, and once in the very sentence in which he mentions the passive voice as a feature of a pretentious style.
This has been noticed (the passive!) by Joseph M. Williams, and he rewrites the Orwell passage, avoiding noun constructions as well as the passive voice:
Those who write pretentiously eliminate simple verbs. Instead of using one word, such as break, stop, spoil, mend, kill, they turn a verb into a noun or adjective and then tack it on to a general-purpose verb such as prove, serve, form, play, render. Wherever possible, they use the passive voice instead of the active and noun constructions instead of gerunds (by examination ofinstead of by examining). They cut down the range of verbs further with -ize and de-, and try to make banal statements seem profound by the not un-formation. (Williams, Style: Ten Lessons in Clarity & Grace, fourth edition, p.6)
Orwell is a terrific writer, and presumably a very self-aware one. It is reasonable to think that he uses the passive voice and noun constructions here on purpose. More importantly, the Orwell passage does not sound pretentious, nor is the Williams rewrite an improvement on it. The reason is, I think, that the subject matter of the Orwell passage is a certain writing style, but the Williams rewrite makes it sound like it is about the people who write in such a style. If the subject is the style rather than the people, then it is difficult to avoid the passive voice and noun constructions.
What we learn from this example is that good writing is not simply a matter of following some rules or principles. There may be rules or principles that you should follow, but what makes you a good writer is your knowing when to break them.