How does academics form discussion & study environments efficiency and effectively?
Let me suggest that there isn't any magic answer. Certainly not for efficiency. But a few things can help. 

Many (most?) such groups have some leadership. Often it is a senior professor and the group consists of other professors and some students.  Often the subject of the group is the main research interest of the senior professor and others are looking for their insights to help in their own research, likely in the same or a related area. Here the leadership is fixed and the cohesion of the group is guaranteed by the stature of that professor. 

Student groups are a bit different. If you can include a professor as leader, then you have a seminar, and many/most of the ideas come from the prof. That can be both stable and productive. 

Some student groups are driven by fear. In some universities, students that don't band together to study will likely be unable to understand everything needed in the course. Some law schools are like this. See the movie Paper Chase for a dramatic example. These are pretty stable and are a way for a group to share out a huge amount of readings and provide summaries for everyone. 

But if you want something more informal, what you need is someone to get it started with some ideas to study and also some commitment from a group of people. Of course the commitment needs to be sustained and that depends on the "work" of the group being mutually interesting. One way to manage the leadership issue is to pass it around. One way to do that is to have people contribute ideas for what should be discussed at the next meeting(s) and then vote among members on what should be pursued next. Whoever contributes the idea becomes "leader" for the discussion of the idea. That person probably has some commitment and the voting may add a bit more. But it is especially helpful if the proposer of the idea can give an initial outline and list of tasks before the meeting(s) at which the idea will actually be discussed. 

This, of course, isn't the only way to do things, but leadership and commitment are, I think, the two essentials.