I'm not a master on building rapport, anyhow these are my tips:
Smile
Keep suitable amount of eye contact
Mirror their posture(bodylanguage), also be careful not to do it excessively, which would backfire and come off as weird.
Uncross your arms
Voice tone (keep same or slightly higher level of voice tone and speed of conversation as the other person)
Lean towards the conversation partner (shows him that your interseted in what he is saying)
Don't blow off his/her perspective to a certain topic (e.g. telling him/her that the music/movie/sport/bar/etc he/she likes sucks or even worse...)
That would be pretty much what I can pull off the top of my head, I hope it helps.
P.S. dont forget to be confident(not arrogant)
Hope this helps
