1) Joomla is based on PHP. Yes, this is an important point because while there might not be a local Joomla users group, there could be a local PHP users group. So check your local area and meetup.com for PHP users/mailling lists and then talk to them and see if there are local Joomla groups(for example, there is a NYC Joomla email list that is practically unknown because it is run by the NY PHP group. When I tell people about it who didn't know it existed, 1 out of 3 people asks me "What is PHP?" - and this includes people running/maintaining/and installing Joomla sites! A tribute to the strength of Joomla that many people don't even know or care what language it is written in!)
2) Get your feedback in steps. I found it best to run a poll asking people what day of the week was best, and after narrowing it down to 2 days, than asking which day of the month they wante to meet.
3) You can't please everyone, so aim to please the ones who actually take the time to respond(I've had a few people comment that the day chosen was bad for them - but if they can't take the time to respond to the poll, the likelyhood of them showing up is already slim!)
4) Better to choose a day and meet sooner to keep interest going, than delay waiting for the perfect day.
5) Be flexible on the day, but not too flexible. The sooner you can establish a single day to meet every month, the more likely people will come in TWO months from the meeting(many people will miss the first couple meetings, but if they know you meet every month at the same time, 2 months later they will have learned about the meeting and will start showing up).
6) Post recaps of the meeting, even if their just short summaries since you don't have great documentation skills. Just saying "We met" doesn't spark any interest, but if you can tell people what you covered at the last meeting - and include the Q&A summaries, than others who were interested in those items may well show up at the next meeting.
7) User types have lives and won't stay late. Developer types have work to do, and will show up late. Leverage this! I try to have multiple presentations and to space them out so the user level presentations are first and the developer ones are last. This way the users don't feel compelled to stay for presentations which bore them, and the developers don't get bored and leave before the presentations of interest to them.

9) Draw on the community for help! This means check out your local related groups and ask them how they got meeting space. For me, once I was organizing I sent email to the local Linux Users Group and the local PHP group asking if they knew of meeting space available and the NYPHP group(http://www.nyphp.org) offered space for our meetings! Once I started holding meetings, a local consulting company offered space for our second meeting(and sprang for snacks).
10) Know your local security issues. For example, in NYC if your meeting at most buildings, you will need to provide security with a list of names they can check for those who are coming. So I need to pester those who are interested to RSVP so we have that list.
11) Don't count on meeting space that will "probably" be available on the day. Take the biggest meeting space you have available weeks in advance and commit to it. You can always change NEXT month, but this month you want to grab people who need to plan in advance.
12) I'm finding doing half hour presentations works well - as it keeps things from being intimidating and lets me strong arm attendees of the events into presenting. If someone can't "present" than ask them to talk about something they did. Call it hosting a discussion on X, as people will chime in with questions and comments of their own and generate discussion.
13) Anyone who suggests you talk about something is automatically volunteering to host a discussion/present on that topic. :-) Don't be too pushy, but do ask.
14) Don't be afraid to cut people off, or bring them back on topic. I find this especially hard, as often I am interested in what someone is saying, but we have to cover multiple presentations. You can always go into more detail after the presentations, but if someone came for a specific presentation, then you want to make sure all of them get covered.
15) I try to have at least 2 half hour presentations in my back pocket to throw in if people cancel or in case presentors are late. If your getting a wide range of people coming, just going through how to install and configure components is good. I don't get hung up on having a GOOD presentation so much as having A presentation. Basically, if you have a GOOD presentation and a GOOD presentor, he/she can cary the meeting and generate interest. But even a mediocre presentation is fine if you take questions, look for answers, and inform people. Someone asks about template design, just saying "I try to avoid it" doesn't help. But saying, "Well, I tend to use commercial templates from template clubs like RocketTheme", show them why you use them and what they do. And take feedback from others and show those templates too! Let people know there are a wide range of clubs out there, and that they should check them out.
16) Questions from the meeting can become presentations for the next meeting. As an example, at our second meeting a lot of people were talking about how to build community sites - and mentioning that there is Commuity Builder for that, right? CB is a great basis for a community site, but out of the box it is not a community site toolset! You need to add other components for that. IF someone installed it expecting a bunch of PMS, myspace, forum functionality they will be frustrated to learn that it is really just a fantadtic user profile tool that lets you integrate all those components in one spot! So, I don't know all those components, but I can certainly install CB, go through what it's out of the box functionality is - and also point out one of the frustrating things with CB - it has it's own plug in system which people often forget!
17) Make sure any urls mentioned at the meeting are in the meeting recap. Be postiive about things that are mentioned if people talked about them positively., As an example, one person mentioned a Joomla web host provider that has a lot of templates and components pre-installed, along with tutorials on their website. Looking at the site, to ME it is a waste of time - but hey, *I* run my own server. To many people just starting out, having a web host which bundles everything together is a HUGE time saver. So I don't use my personal judgement on things that are mentioned, but make sure to get feedback from the members and present it in the summary.
18) Thank your host! Even if the room was too small, they offered and were instrumental in making things happen. Better a too small room than NO room.
19) Clean up your meeting space. This should be a no brainer, but people who leave early will leave kibble behind. Clean up after them.
20) If meeting at an office or such, make sure to scope out the area beforehand and find a place to go hang out afterwards. Find out what people want who will actually go! For example, I'm perfectly happy with Starbucks or Barnes and Noble - but the people who hang out afterwards at my meetings like to have a beer and relax a bit. So I go with the local TGIF(they ahve an onling restaurant finder).
21) Be a card person. Print up some cards with your name and email address on them for the meeting. This way people can contact you afterwards to find out when the next meeting will be.
21) Be a considerate host. If your pushing people into presenting, buy them a beer/coffee/whatnot afterwards. It's a small price to pay to not have to fill 2 hours of time with your own talking.