Realize you have a head start when you have already been talking to this person even if it is on line.  Just walk in there and be yourself as I hope you have been while talking to him on line.  If you are then you have nothing to worry about.  If its your looks I hope you walk in there being proud of who you are because there was something about you that got him to the point of wanting to meet you.  RELAX and enjoy the time