Rapport in NLP is the presence of trust, harmony, and cooperation. In NLP Training various techniques are learned how to establish rapport, quickly and effectively. Rapport is not a step, it is something that needs to be achieved and then maintained.
How do you know you have established rapport? A way to know you have rapport is that you can pace and lead a client. Or in non-NLP terms, you follow your client in whatever it is they verbally or non-verbally do and then then you lead them in to doing somethig else unconsciously. When they follow you, you are sure to have rapport.
One way of establish rapport with a person, is to match their breathing. Breathing at the same depth, at the same speed, same intensity, and from the same location.
When your significant other next to you is sleeping. Match his/her breathing for a minute or two. Then breath faster, and notice if he/she starts breathing faster. Then slow your breathing, and notice what happens.
I love pacing and leading my clients breathing patterns.
It helps me:
To establish rapport
To know if I have achieved rapport (by pacing and leading them)
Calibrate to their given state
Understand the client, and what physical reactions occur within me, breathing at that rate (not enough oxygen in to the brain causes a feeling anxiety.)
Pace and lead the client in to slower breathing to help them relax. Or speed up their breathing to elicit a state of for instance excitement.
Another way to establish rapport through breathing, is to tap your foot at the same rate. Then slow or speed up your tapping.
With so many people being informed of matching, mirroring and cross-over mirroring people are increasingly becoming too aware of the technique (even though this occurs naturally as well.) Matching breathing is very hard to detect by another person, and an incredibly handy tool to use.