There are two - the first one was my inviting the groom's son onto the stage (he was 3) to assist me in asking people over the microphone to welcome the bride and groom for the first dance. He forgot his words and I helped him, it was very cute, very funny and very well filmed and the groom was in tears.
The 2nd was being requested to play a track by Lulu for the first dance from around the late 60's (bride and groom were under 30), to my amazement the dance floor erupted with all of their guests and it was the most amazing first dance!
Professional, knowledgeable, trust, communication skills & a smile!
By being able to read the crowd and recognising what they want to hear. Having a diverse database of tracks is very important and so that everyone leaves feeling they had an amazing evening