Johnson feels his career is back on track after quitting Manchester City.
He told The Sun: "He has a friendship with the players. You can talk to him about anything really, it doesn't have to be football.
"He gets the best out of players, he knows when to shout and knows when to put his arms around players. He does that very well.
"After speaking to Martin O'Neill, he makes you know he wants you and he makes you feel 10 feet tall. If that's how a player feels, that's when you play your best football."