By way of introduction, I am the current President of Linux Users of Victoria (Australia). We have two meetings a month, a main meeting with two talks (nominally intermediate and advanced) and a beginners workshop. We usually organise Software Freedom Day (do this!), and install-fests and miniconferences in regional areas - so far we have chapters in Ballarat, Geelong, Shepparton, and more coming. We've been around since the early 90s and have around 1500 members.
From my experience in LUV and many other community groups there are two key things that keep a group going.
Somebody has to be a leader. Better still you can have multiple leaders and distribute tasks between them. Leaders are the people who will ensure that the meetings happen, that events are advertised and so forth. They are the public face of the organisation and they must work to improve the organisation every day.
Leaders also must be very, very attentive to their membership. A leader cannot exist without followers. Always listen to what others want to see happen. If someone has an enthusiastic proposal, delegate authority and action to them and help achieve their goal. Also, leaders don't give up.
A society survives because it generates a culture at a community locale (real, virtual, or both). What is the core ethos of your society? From what you've described, you need to need to both interest and differentiate from the existing computing groups. If they other computing groups are into mobile web there's not much to be gained on replicating that. I would suggest a key feature of Linux that has broad popular and technical appeal is the notion of software freedom. Make that your driving and motivating force. Even if it is three people sitting around a coffee table discussing the latest version of Firefox, the fact that they have come together in the name of the LUG to discuss a matter of common interest means that you have a group.
Provide leadership and ensure you have a community and everything else is detail. Also, feel free to contact me lev at levlafayette dot com for any further advice.