Something that should be hashed out at your first writers' group meeting is the question of how often you're going to meet.
This is going to vary, depending on the number of members and their schedules. I mention this because the group I meet with has met every three weeks for the past eight years. That works out best for us, who seem to have very busy schedules (working two jobs, raising a family, etc.). It also gives us time to polish up our next piece and continue working on other projects we're not sharing with the group.
Some groups meet monthly and others I've known meet biweekly--on a side note, I listed to a writing excuses podcast (www.writingexcuses.com) where the members of that podcast attend weekly. Keep in mind, those are published authors, but it's something to think about if you want to be published. When we met, we thought monthly was too long of a break between meetings and every two weeks seemed tobe too often.
Typically, we've averaged four to six members at a time. Here is what we do: after a quick greeting, we see who brought stuff to read. Most times, everyone has something, although not everyone attends each meeting. Then, whoever has something to share, passes out copies of their work and then he/she reads their piece. Afterwards, we critique what worked and what didn't, the story's strong points, and if there are places that need revising, we address them here. This process can be cumbersome, especially if all five current members share something--three of us are novelists so sharing entire or partial chapters can drag these meetings out. In the past, we've tried handing in your work to the librarian a week prior to our meeting, and although this worked for a little while, it also proved troublesome because not everyone was able to get their work to the library and the library was really open after 5PM one night a week. If it works for you though, that's great. At least try out different ways to share your stories.
How often you meet doesn't matter as much as it does one's commitment. You should commit to attend every single meeting, even if you don't have something to share. You're still able to critique others' works and hopefully inspire you to bring something next time.