The more folks we know, the better the event. Our first event, we knew no one. We were also the only non-Germans, and felt awkward not understanding most of the conversation. But everyone was very nice and welcoming, so we warmed up. The next several events we attended went much more comfortably once we knew what to expect.
I think we tried a little too hard as hosts on our first couple events; we had games, new caches, and prizes. That said, everyone had a really good time, and the games really helped the crowd mingle, since there was a mix of US military geocachers and local German cachers who I'd met at events.
Since we move around every couple of years, I've found events critical to get to know the local community. It's the best way to break the ice.
All that said, I still think the favorite event we hosted was our 10 Years! event in Charlottesville, Virginia. Everyone was excited because of the icon and the theme. We had a special cake, and everyone had fun grilling out and having a picnic at the park. We had a few new caches hidden for the vent, which people enjoyed. It was a relaxing day for everyone, and in an area that didn't have many caches or events, I was pleasantly surprised at the turnout. It seems like geocaching really picked up steam around there after that event, and if we had a little bit to do with that, then I'm proud of that.