When people spend a lot of time together, they tend to share mannerisms, reactions, vocabulary, and tone and speed of speech. You can see this with good friends, couples, and relatives. If you match and mirror someone, they will feel a lot more comfortable and relaxed with you and like they have known you longer. Do this by:
Speaking at a similar speed, and using a similar amount of gestures.
Feeding back the words they use in conversation.
Mirroring the way they sit, the amount of eye contact, and the facial expression.
You can get away with a surprising amount of mirroring and matching – they don’t seem to notice!