When I was in high school, I didn't have many choices on what classes to take. I liked it. When in college, I had some more flexibility, but much of the guess work was taken out: take 3 classes, 2 classes, and then 3 classes each tri-mester and I would graduate.
When it comes to teaching or leading a small group, choosing what to teach next can be difficult. Here are some guidelines that help me think through what to teach next. They are not from Mt. Sinai, nor are they ordered in any sense of primacy. But cumulatively they can be helpful to make sure that you are teaching on a variety of different, relative subjects, moving those under your care towards maturity in Christ (Col 1:28-29).
Some churches have designated key areas, and leaders can choose a book from each key subject area. One of my churches I served at had 10 separate keys that would take place over 3 years. Then you repeat. This method is thoughtful and ensures that you cover a variety of issues-some of which you or your group wouldn't choose but nevertheless needs to discuss. While this plan makes sense, I don't know if it is absolutely necessary. That church tried this method, but not for long. Systematically going through topics is grand, but I just don't think you can cross subject matters off the list and then move on. That's why I prefer something a little more flexible.
1.) Bible. In college, I remember a bible study that I went to once. They challenged everyone to take seriously, very seriously, what we would be studying for the next semester. Like we could end up studying the wrong bible book. I thought, well, if its the bible, that's probably good. They didn't think that, but I still do. I've never studied through a book of the bible and as a group discerned, "This really wasn't relevant. I think we should have studied a Pauline epistle instead of James...." Never. The Good Book Company and Matthias Media has all kinds of great bible study guides.
2.) Have a frame-work. While I don't think you necessarily need to be locked down into a systematic grid for what to study over the period of 5 years, I still like having a framework. We should have in mind issues and topics to consider for our next study or discussion. If you don't have any framework in mind, you may tend to skip over some issues you could have ignored. The framework I think through is the Head-Heart-Hands Model. Is there anything that our group would benefit from knowing more about God (Head)? Maybe we need to spend some time on Christology because people don't understand who Jesus really is (Head)? Are there any Heart issues, like materialism, worship of family, which could be best tackled through a specific book or study? Is it best to continue to lay a gospel foundation, which people may not really grasp (Heart)? Are there any practical (Hands) issues like how to parent, do finances, how to study bible, how to share your faith, how to show mercy, etc...? I tend to reserve the latter two for small group and the former for Christian Ed/Sunday School. If you tend to study practical issues in books, then its probably wise to take a break and simply study the bible, books, or studies particularly plumbing the depths of the gospel. If you've never gone theologically deep (Head), but focus primarily on the practical and outreach/mercy (Hands), then it might be wise to balance. A framework can help that.
3.) Freedom: Those who oversee certain ministries have the final say on what gets studied. That's their "job." I prefer to give leaders lots of freedom because they are at ground level, hearing what is being discussed. They hear the answers. They know if the group lacks knowledge (Head), the application of the gospel to life (Heart), or if the group knows anything about tithing, showing mercy, reaching out, whether they are serving their church. So as a leader, you just want to have these things in mind. You are a student of your group, as much as they are a student of your teaching, leading, shepherding.
If you are attentive, you will begin to discern heart issues, growth areas, application blind spots, areas of scripture (all of the aforementioned you may have too!) that you'll want to keep in mind for the next, as well as the current study material.
Some questions that can helpful to think through are as follows:
a.) What keeps them up at night? What scares them? In other words, what are their idols? Respect, work, love from spouse/family/friends, family? Anything that if taken away, would leave them with no reason to get out of bed.
b.) How well do they know simple truths of the gospel? Are they ready to move deeper (not advance beyond)?
c.) Does any theological question keep coming up? Is there any section of the bible which they seem to deficient or interested in knowing more?
d.) Are they interpreting and applying the bible in a Christ-centered way or simply as instruction manual?
Some things may be more pertinent or pressing to study than others, so that's why I like to get input from leaders.
4.) Asking: Much of the time you can get what you need to study by thinking ahead of time where you want the group to go, and then tweaking that plan if need be, by your attentiveness to their needs. However, another way to supplement (not replace) is by asking them. It can be helpful to ask if there any issues or sections of the bible which you feel you need to study? This can sometimes be quite helpful. Or you can ask something like this, "Would you be interested in studying a book by so and so?" I did this and it let me know NOT to go through a particular book because they wouldn't have time to read it. I'm glad I asked and I appreciated their honesty!
However, you also need to be aware that sometimes people will pick something that he/she wants to study but the individual, or the group as a whole might need to study something else. For instance, someone might want to study "end times" or "prophesy" when in reality, he/she doesn't know his spiritual gifts, or is shacking up with his girlfriend or boyfriend.
5.) Sermon discussion/application: I've never done this in a small group bible study, but many churches do. My last church did this off and on in Sunday School, which took place after worship. Many enjoyed and benefited from it. The Mars Hill churches have this as a regular component of their community groups as do a number of other larger churches as well as thriving church plants. The idea here is to focus not primarily on what has been said, but to believe the truth that has been preached, and apply what has been preached. This of course requires that your group is regular in worship and the leader takes notes and asks good application questions.