Originally being a Don was regarded as being close to be a God because of the intelligence of the Boss. As Goodfella 69 said, you have to be a fox and a lion(As Carlo Gambino´s phrase claims).
You cannot trust anyone, even your children, wife or closest friend.
You should shut up your mouth more than you speak, you have to say what the people around you want to hear, I guess the main point is that you have to live today as if it was your last one. You could die anytime, remember you have people uder your control that want to take you away to be the next Don, for example in the real Life(Paul Castellano-John Gotti, Vincent Mangano-Albert Anastasia-Carlo Gambino, Joseph Magliocco-Joseph Colombo, Frank Costello-Vito Genovese).