I have started several groups, whether for critiquing, RWA, SinC, etc. What I have done is placed an ad in the local paper and set up a place and time, and what the meeting is for. From there, people show up and we get to know each other. When you discover the ones you feel you can trust, you ask them to read your work and vice versa. We set a two week period and then exchange back the work with comments, marks, and much more. Or, we have a yahoo site from which we can download each other's works, make track changes with comments and a quick phone conversation and go from there.
Sometimes the group gets too large, or someone is too critical. Guidelines need to be set up before exchanging works, And you can set how often you want to meet.
I have a particular group who have become good friends. We read each others' works and meet up 3 times per month. We also do 2 retreats a year just to focus on the writing craft needed in each project. Not all groups will work for all people.
The total group has expanded to more than 20 people and there are so many different genres and personalities, that working groups have been teamed from each genre. Also, the craft of writing has several different categories beginners, experts, part-timers, real writers and dabblers too. So, each group tends to help out the other. And it can get long if everyone decides to contribute at the same time.
As Jordan has said, it also depends on your needs. As your skill develops, your needs change. So does your "group." They can be a source of great inspiriation. Five members have been published or offered a contract in the last year from within my group.. That's a motivator for everyone in the group.
Stephen has raised great questions for you to investigate. They should help you find what you need and what will work.
My wriuters' group is in the form of classes at the Council of Adult Education. Our Popular Fiction group began the year with 18 and we have only lost two who couldn't hack the pace and demands of regular writing. We are set class exercise each week to warm us up and then there are intense workshopping sessions in which we critique and advise. Many useful observations come from these sessions, especially as they are done in a co-operative, supportive fashion, intended to encourage rather than deter. And strangers are much better and more honest observers of your work than relatives and close friends.
I agree with Dean Koontz and believe that writers group do more harm than good because you're writing for that group, not a larger audience -- and writer groups can be very clique-ish. Right now, I have three readers. Two of them I work with at my day job, and the other is an old college roommate. In the future, I'd like to get two more readers, but I thought the three of them did a good job with the latest novel I'm working on.
Yes I'm in one now and have been in one or another for over 4 years. I found my first through Writer's digest Magazine (hard copy). Every year they list the top sites. Unfortunatly m,y first group I joined is now closed. Members of this group started their own group and arre doing rather well. If you're looking to join one be sure to check them out. Look at the replies the members post especially the critiques. Do they rip the posts apart along with the author or do they offer constructive helpful comments. Also be ready to comment enough time to the group. Most want you to do atleast 2 or 3 critiques before you can post a chapter or section of a chapter of yours for other members to critique. IMHO this is only fair.
I hope this helps
G W pickle