I have belonged to a writer's group for well over a decade. Sometimes called critique groups, writer's groups are one of the most powerful tools a writer can have— if he belongs to a group that works for him. The wrong group is worse than no group, but the right group is a treasure.
Our group has minimal rules. We let writers submit short stories or novels, and the novels can be submitted in chunks as they are written, or as an entire manuscript after they are complete (although those require at least two months reading time). We don't require a specific number of words from every writer, and although we are all speculative fiction fans, we will look at mainstream work or stories in other genres. Critiques are presented at a more-or-less monthly meeting where we go around the room, but unlike some workshops, we don't impose a strict “absolutely no comments or questions while the critiquer is speaking” rule. The writer and other critiquers can speak up if they feel so moved.
The membership has fluctuated between six and twelve members over the years with people dropping out when they get too busy and sometimes dropping back in as their circumstances change. There are a few members who have been in the group even longer than I have. I have stayed in the group because I find it valuable, and sometimes I find myself harking back to other people's comments on mine and other member's stories, some of which we have solidified into “X's rule.”
The Kathy Rule
If possible, don't give minor characters a name. Referring to them by name signals the reader that they have some importance, that they are worth keeping track of. If characters aren't actually important, try to avoid naming them.
The Sharon Rule
In writing spec fic, avoid figurative verbs that could be taken literally in some circumstances. That is, don't say the hero flew across the room, or the heroine vanished from the doorway, unless those characters are literally doing what the verb says. This is especially true in the first few chapters where the reader is figuring out the rules of the world the writer has created.
The Tom Rule
The protagonist must protag! That is, he or she needs to be an active player in his or her own destiny. Circumstances might force an unpleasant choice on him or her, but the protagonist needs to be the one making the choice.
The Carmen Rule
Avoid flashbacks, when possible. This is partly personal preference, but I do generally prefer a linear story line, so long as this allows the story to start at a good place.
Of course, like any good rule, any of these can be broken by a good writer!