George Orwell's, "Politics and the English Language" no-nos:
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.
Note: This would actually be my #1 pet peeve, if I wrote the list. I can't stand writers who use big words for the sake of using big words, as if their ability to navigate a thesaurus would impress anyone.
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.
Note: This is my #2 pet peeve. Passive voice is lazy writing, boring and something I associate with manipulative people. Hate it, with a passion.
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.
When my college classmates would ask for my secret to getting high As on writing assignments, I always told them to read the Orwell essay, and then follow its advice, anytime they put pen to paper (or fingers to keyboard).
That one short essay will make anyone a better writer.