Indicates someone may act arrogantly due to a recent achievement or compliment. She won the chess tournament and it has definitely gone to her head.
Pro Tip 2/3
Warning of Humility
Used to caution someone not to become overly proud or to expect too much from early success. I’m happy you got the promotion, but don't let it go to your head.
Pro Tip 3/3
Social Caution
May imply the person could become or is becoming unpleasant to be around. Ever since he became manager, power has surely gone to his head.