#2 Watch and learn

John Cena has masterfully handled the polarizing response that he receives from the WWE Universe for a number of years now.
He knows how to make an impression and get over with the audience regardless of the kind of feedback that they throw at him.
Female superstar says she inspired John Cena turning heel HERE
That is an invaluable lesson for Roman Reigns to learn.
We often see Reigns getting put off when the audience doesn't react the way he expected them to and, in the process, give them more leverage to try and unsettle him.
What he needs to do is ensure that he's the one who's playing the fans and not the other way around.
And there's no better person to learn that art from, other than the master that is John Cena.