I have a few minor rules for myself but I break them all the time. For example, when translating from Romance languages to English, there is often a choice between a Latinate cognate and a Germanic equivalent. An easy example would be the Portuguese escuridão: English offers both obscurity and dark or darkness, and some translators will tell you the Latinate word is generally reserved for poetic and figurative expressions, while the Germanic word is used for colloquial and idiomatic use.