1 - Don't leave your guest ponder. If they show up, greet them and let them know that they are in the right place. A lot of programming meetup I went to lacked a lot of common sense. This is one of them.
2 - Have things to discuss about and not just say "come, code". Do something with them, get people to share their projects, get talking. I get the impression that coders are know it all, so they don't talk.
3 - Get a place that is easy access by bus and parking with plenty of space. Make sure that you are visible and not some kind of coffee shop in the back corner without telling anyone.