How we change what others think, feel, believe and do
'Mirroring' is copying exactly what the other person does, echoing their body language and other non-verbal communication, including sounds, voice tone and so on.
Mirroring has a 'sidedness' to it: if they do things with their right hand, then you also can do things with your right hand. Alternatively, you can do it with your left hand. Sometimes this is a natural action -- if you are both right-handed, then you will both pick up something in your right hand.
Mirroring can be done at exactly the same time (which needs quick reactions!) or may be delayed. Often, it is best done with a slight delay to avoid appearing to be copying them.
The best way to use mirroring is to copy the less overt movements and sounds, and at selected moments when you want to achieve maximum agreement.
If they cross their legs, you do the same. If they scratch, you also scratch. If they cough, you cough too. If they frown, you frown. If they talk fast, you talk fast.
The basic principle of mirroring is that when the other person sees you, they also see themselves, which is an attractive image.
Mirroring works only if done subtly and not excessively. If you over-do this, it just looks like you are aping them, which can be taken as an insult and have the reverse effect to any intended bonding.
Mimicry creates what is called 'sensorimotor fluency', which basically means it is easier for the brain to process something that it has just initiated in its own body. This leads to comforting feelings and consequently increase liking of the other person.
Mirroring is, in some ways, the non-verbal equivalent of parroting.