If you're thinking of joining or starting a writing group, it's best to have your focus in mind right from the beginning. The basic commonality is that writing groups in general consist of writers.
(Don't you already feel enlightened? Well read on!)
Because that's pretty much where the commonality ends. Let's check out three distinct species of writing groups.
The first species is what I'd consider a support group. The focus is social: the writers gather to gripe about writing. They will perhaps come up with an organized topic of the day, but for the most part this group is about the snacks, the sharing, the complaining, and some exchange of advice. Its function is primarily to meet other writers and to get out of the house.
Some of the topics you'll see covered here are how much rejection sucks, how hard it is to get things published, why is that particular crap in the bookstore when yours isn't, what you think of the recent election, and whether there's really a problem with that genetically-altered corn. You may also hear about places to search for markets.
If this group is online, then expect to read dozens of posts about everything under the sun, and whenever someone complains that the group is too cluttered, someone is sure to respond, "But we're writers -- this is what we do!" My first online group was of this variety, and I loved it. I learned a metric crapton about everything you can imagine, including some tidbits about writing.
My once-thriving group was also a social/support group type. Sixty local writers would gather, always with coffee and muffins, and sometimes they'd share a paragraph or two, maybe a poem or a letter to the editor, and everyone would tell them how lovely it was and suggest changing a comma in the second line. Someone might give a brief talk, at about the depth of an article in a writing magazine. There was a break in the middle so we could chat.
When I joined, one of the members told me, "This group is for everyone from multipublished journalists to little old ladies writing poetry for their cats." Even their critique guidelines were flowery and overwritten, but the group itself was positive, supportive -- and it thrived. When four of us wanted mutual assistance on novels, we split off to form a novel critique group that met after the main meeting.
This leads to the second species: the critique group. My current group is critique-only. The membership is limited. Two weeks before the meeting, the leader distributes the pieces we'll be
[Please note: I'm really tolerant, but if you ever end up in a critique group dominated by nastiness and negativism, thank them for their time and don't come back. There's nothing to be gained and everything to be lost when writers gang up to punch a newcomer's manuscript full of little holes just because it's fun. I can still remember one particular group leader looking at a manuscript as if it reeked of vomit, then growling, "This is crrrrrap." Run away. Run like a citizen of Tokyo fleeing Godzilla.]
The third species of writing group is the instructional group. In this, your meetings resemble classes. The instruction may involve some degree of critique, but it's within the narrow guidelines of the lesson. This week we're working on point of view, everyone, so get out your notebooks and write a third-person paragraph about a man whose wife has just died. Now write it from someone else's perspective. Now I want you to combine those pieces and deliberately head-hop, and let's see how that affects the work.
Like a critique-only group, the instructional group will focus on improving your writing, but you won't learn by comments specific to your own piece or by interaction. The benefit of an instructional group is that you don't have to show your own writing to anyone else in order to reap the full benefits of the group.
These varieties of groups (and their hybrids) fit different niches, and all of them are useful. If you're just beginning to write, for example, maybe you're not yet ready to receive critque, but if your group's structure enforces sharing, your writing will be exposed at a time when you still feel vulnerable. (You'll always feel vulnerable. I mean especially vulnerable.) Or if you're ready for a black-belt level beat-down of your manuscript, a social group might leave you restless.
Now, how to kill a writing group in three easy steps? Actually, one easy step. Take your sixty-member social group, which has remained largely unchanged for fifteen years, and force it into an instructional model. In our case, the purely-social members drifted away after the first two lessons. After six months, the group leader was assuring those who remained, "We'll have a core group of highly-motivated writers." I kept believing her right up until the minute I couldn't any longer -- when she left. The members hadn't been coming for high-tech instruction. They wanted the coffee and the cameraderie.
If you decide it's time to seek out a group, whether online or in person, be open to what that group has to offer rather than forcing it to fit your preconceived notion. Figure out what this group can offer and what you can offer the group. Then be flexible: you may discover a critique group isn't what you're ready for yet, or you may feel unfulfilled doing nothing but socializing. On the other hand, you may discover the perfect critque partner in that social setting. Opportunities are everywhere if you accept them for what they are.