You might select one behaviour per day to practice until you can build a whole repertoire of rapport skills. Move your foot to pace another person's head movements. Tilt your shoulders slightly as the other person tilts their head. Lift a finger as the other person lifts an eye-brow. Also remember to practice mismatching, but be sure to end the interaction in a state of rapport.
Some people feel they just have to match and mirror.
A young woman who matched and mirrored constantly was sitting across from a colleague who was tired of being mimicked. The colleague slid down in his chair, and of course she did the same. Then the colleague slid down even farther. She did the same. Her colleague, conscious of his mirroring, remained in his chair.