First, make sure the event is worth going to. The launch event of a weekly or monthly group meeting has to have some spark and incentive in order to get off the ground. If you can affordably cater the event (offer free food), that will help quite a lot. In your case, one of the signature events of a LUG is an installfest where Linux experts help Linux newbies install a desktop distribution on their computer in a dual-boot configuration, or they set up a USB drive to provide an alternate boot option. If you can afford to cover the cost of pizza and soft drinks for the attendees, and offer to perform free data backups to DVD (bring a spool of blank DVD-R discs), those would be two excellent, inexpensive incentives that would drive participation.
Think about the subject of an installfest. You need people who know Linux, and people who want to learn Linux. Where would you find people who have interest on both sides of that operation? Computer repair shops, perhaps. Can you post a sign or flyer there? What about at computer stores? Perhaps the owner of a small local shop will even offer to cover the cost of the refreshments if he’s allowed to bring some demonstration models and service flyers to the event.
It’s possible that you can leverage an existing technology-oriented group on Meetup.com as well. Search through the site and see if you can find related groups, then contact the group organizer and see if she’s amenable to your hosting your own event through that group.
In general, local events have gotten a little tougher to promote because local periodicals have lost a lot of popularity and relevance. You can’t take out an ad in the newspaper and expect results from it anymore. However, there’s Craigslist—that’s free, and has a lot of reach in the metropolitan areas that it serves. Post an ad there and keep it current right up until the actual day and time of the event. Then for the next meeting, post a different ad with photos and praise from the attendees of the inaugural event—social proof that this is a fun and interesting group that real people attend.
Also try to reach out to local bloggers; search all of the blogging services (e.g., WordPress, TypePad, Blogger) for people who are in your area and might have an interest in your event. For technical events, look for local blogs through Technorati.
Create a Facebook group for your meeting, and on the night of the event, take pictures and short videos and post them to that group. While you’re among the attendees in person, go around with your smartphone or tablet and invite each of them to the Facebook group and ask them to post something and invite their friends. After the first event, you should have enough momentum to see a benefit from spending a little bit of money ($20–$50) promoting your Facebook group to continue to improve attendance. Remember: you’re always looking for new members, even if you feel that you’ve achieved your attendance goals!