Adding to that here's a few things we've learned about hosting good meetups from starting Jelly in Chicago...
Consistency is #1 - have it on a consistent day and time at the same place every time you do it, especially in the beginning. Its easier to spread it by word of mouth this way and easier to catch people who just show up because they heard about it
Having it in a public place with the possibility of food and drink is incredibly important
Do not publicize it to anyone but your friends and acquaintances, keeping it to people you know is a good group filter. The way it grows is everyone who comes invites their friends too and you meet their friends, friends of friends etc...its a simple quality filter that can grow very quickly. friends vouching for something is the best way to verify that its worth your time as well. To this end, twitter is easily the most useful tool for this type of meetup (this may be a chicago thing as all sorts of people flock to any event on the radar since we only have a few)
That said, welcome everyone who shows up.
NO PITCHING NO SELLING, HAVE FUN, good business relationships come from people you know and like not people you sell too and trade cards with
Have the meetup even if only you and one other person show up and keep having it, people will come eventually and even if they dont you still hung out with a friend for a while. People get discouraged if you let the meetup lapse. A new person showing up to zero people will have a negative reaction but showing up and meeting 2 people makes it a worthwhile night for them. Meetups are like startups, sometimes in the beginning you just have to do it even though no one seems to care or be paying attention, hang out with smart/good people and the word will start to spread
* We don't set a hard and fast date (although we try to keep the time and place regular). NYSEC does a "second Tuesday of the month" thing; there's more security people in NYC, but our attendance is often 2x theirs. What we do instead is a mailing list and a website, and we poll the group members about what the best date is. 8 months in, we switched from Thursdays to Wednesdays, for instance, and got a significant boost in attendance.
* We publicize. Why wouldn't we? Sure, you want good people there, but the idea that there even is a "group filter" is a deterrant to newcomers. And what's more important than a group filter is attendance.
I actually don't think showing up and meeting only two people makes it a good experience for a newcomer; I think it ensures that newcomer isn't coming back next time. Better to skip a month or two than risk new people having that experience.
i should add that its important to determine what the people who start the group want from it in the first place... ever been to a tech cocktail, silicon prairie social, or social media camp event? The lack of quality interaction that exists there is one of the reasons we choose not to go crazy with publicizing
second tuesday of the month or whatever meets the consistency principle, note that you didn't switch until the event was established
the number of people needed to make it worthwhile depends entirely on the frequency with which you have the event
