These events ran for a while this summer until the Goethe Institute could no longer accommodate us. I attended several, and they were a lot of fun and good practice. It is one of the best events for speakers of mixed levels, and I have some word games we can use to get conversations started.
The two issues have been a location (which we have now), and making sure someone attends who is fluent or a native speaker, because someone almost always can't remember the gender of a noun or a particularly obscure word. If we get someone that facile with the language to attend, then the event will happen. Otherwise, I'll have to cancel it.
You can be at any level of study, but at least a basic vocabulary and sense of grammar helps. You may otherwise want to bring: a notebook, a writing implement, and perhaps a German dictionary, book, magazine, or newspaper. If you want to prepare, try to be able to answer in German at least some basic facts about yourself, like where you live and what you do for work.