Don’t show off your vocabulary. Reading infrequently used words requires more mental work than reading common words. This slows down readers and makes your text hard to understand.
Keep it simple and stupid (the KISS principle).
Use words that are common and short. Use uncommon and long words only if there is no simpler alternative.
Bear in mind readers who speak the document’s language only as a second language.
Typical examples of words that you should replace with simpler alternatives are nouns with 3 or more syllables and foreign words.