Form a group with serious members only. The point of a writer's group is fixing your writing. Form a group that will achieve the goal. Fourth, avoid a writer's group that only functions as a mutual admiration society. Writers do need to stick together in the face of the megalithic publishing industry, and a good shoulder when the rejections arrive always helps.
Mutual admiration helps nothing but the ego.
Marketing advice forms an important part of a writer's life. Still, writing well must be the main focus of a writer's life, and it should form the basis for a group. Belonging to a group which chases off after the latest trend in publishing helps no one. Again, stay focused. Self-criticism can sometimes get a little too harsh.