In business or in life? In my business (nursing home), my best advice was from my grandfather "Treat every one of these residents and their families like they were your family". It sounds pretty elementary but you'd be suprised at how easy it is to caught up in the day to day. I make it a point to visit and sit with my residents on a daily basis regardless of mental status.
In life I'd say "Always keep your word", again a very basic thing that should be a given, but unfortunately so many seldom do.