"We are writers with a good grasp of the writing process, coming together to share tips and tricks, and share brief excerpts for constructive criticism."
It would possibly help if you specified that "good grasp of" meant intermediate to advanced. With writing and the group as it's structured, in as much as there's structure, there's very little functional difference between including an intermediate writer and including an advanced writer. It's a lot different to include a beginning writer or a non-writer in the regular function of the group, though when you suggested that we could invite beginning writers or non-writers to sit in (rather than actively take full participation) that opens up the possibility to better include them.
In case you can think of anything else to say about the group that would fit in the catalog, I'll describe what we do a little more completely.
The format is flexible and takes into account the dynamic needs of the group from meeting to meeting. A typical evening will start out with anyone who has news or items of interest to share talking about it; this can range from talking about global or local writing events, informal chatter about writing projects, to updates on personal situations. This lasts anywhere from ten to thirty minutes, depending on group size and focus that night. Sometimes there is a writing prompt for inspiration for anyone who wants to use the time to write something quick.
After critical mass has been achieved, I take stock of the group size and how many people have brought some piece of writing to share. I decide on a time limit for sharing, announce what it is, and open up the floor to anyone who has a piece of writing to share (or some writing concept or difficulty that they need to bounce off the rest of the group, though this is a little less common). Sharing commences. I set the timer on my cellphone as an impersonal and impartial judge of time limits.
After or during the time someone is sharing their piece or writing problem, there is constructive criticism and friendly deconstruction. If no one can think of something nice or even constructive to say about someone's work, there is an awkward silence, but usually there is a chorus of commentary, both about strengths and weaknesses. As a writer advances in her craft and self-confidence, we become more focused on isolating any weaknesses in the writing and helping overcome them. If we sense that a writer has doubt about her ability to write, especially doubt about her ability to write up to the level that some of the rest of the group is writing, we encourage her in the strengths that we can identify. This is where the true strength of the group lies, because everyone brings a different perspective to identifying the good parts and suggesting improvements. If commentary runs extremely long or the group digresses, I pull us back on task, and we move on to the next person.
In the event that there are only one or two people with anything to share, we focus more on the support of the writing process, inquiring about current works in progress and their status, trying to break down creative barriers and suggest new angles for something that isn't working out as planned. This is the other strength of the group, though it's a far more elusive one. Sometimes no one can help; sometimes it turns into an incredible session of creative breakthrough.
Virtually the whole group participates in NaNoWriMo, National Novel Writing Month, the 50,000-word novel challenge that takes place in November. The official nanowrimo.org's challenge is to write an entire new novel, start to finish, from 12:00:00 AM November first to 11:59:59 PM November 30th, but we don't always play quite by the rules -- works in progress are welcomed, as are non-novel substantial creative efforts. Group format can fluctuate wildly in November. I team up with one of the official NaNoWriMo municipal liaisons, and we work at active support of the marathon novel-writing process in November. Sometimes the group needs to share and get focused feedback like is normal the rest of the year; sometimes the group needs an oasis of writing space out of the chaos that their week turned into.
I'm very glad that you're allowing the writing group to have so much leeway with how we do things, because we're having an incredible amount of fun, and there's so much writing and growth going on.