Ask professional writers to describe effective writing and they'll give you more answers than you need.
That might suggest that they don't agree on what makes writing effective. But they do agree. They just use different language to describe what they do and like to read.
Intimate? Yes. Like one person talking to another.
Whether you are writing to hundreds or one person, it's the same. Your audience should always be thinking that you are in a conversation with them individually, not addressing the nation.