This strategy is called mirroring, and involves subtly mimicking another person's behavior. When talking to someone, try copying their body language, gestures, and facial expressions.
In 1999, New York University researchers documented the "chameleon effect," which occurs when people unconsciously mimic each other's behavior. That mimicry facilitates liking.
Researchers had 72 men and women work on a task with a partner. The partners (who worked for the researchers) either mimicked the other participant's behavior or didn't, while researchers videotaped the interactions. At the end of the interaction, the researchers had participants indicate how much they liked their partners.
Sure enough, participants were more likely to say that they liked their partner when their partner had been mimicking their behavior.