Speak the other's language.

A simple truth: people are more likely to trust those who are similar to them, whom they can understand. So your task is to adapt to your interlocutor. She quotes the greats? Try to remember a couple of them too. He jokes? You also need to show your sense of humor. This rule applies to non-verbal communication as well. If the person is actively gesticulating, then you need to be lively and open-minded. If he/she chooses closed postures, you should be more restrained. This method also works in a group. You just need to find out the manner of communication appreciated by the particular audience.