Question: what are the principles of effective written communication?
Answer: Brevity. It is bad manners to waste [the reader's] time. ... 
Clarity. It is bad manners to give [readers] needless trouble. ... 
Communication. The social purpose of language is communication—to inform, misinform, or otherwise influence our fellows… . ... 
Emphasis. ... 
Honesty. ... 
Passion and Control. ... 
Reading. ... 
Revision.