When you are teaching adults, you are doing something which is entirely different from teaching children and teenagers: you are teaching your peers. Because of this, there are some very wise words from scripture that apply (although you may never have thought of these words in this context!) In the Sermon on the Mount, Jesus said,
Since the adults are your peers, every time you get up to speak, you should ask yourself this question: If I was in the audience, instead of behind the podium, what would I want/expect/need? If you can answer that question for yourself, you will be very much ahead of the game when it comes to teaching others. When I ask this question, I come up with some very basic and simple guidelines.
Don't: Waste My Time
This goes right along with one of the important lessons for teaching teenagers. Your audience is not there simply to be entertained. They are there because they have a hunger for something more than what the world is offering them.
Does this mean you shouldn't try to be funny and entertaining? No, it doesn't mean that. What it does mean is that even your humor should have a point. Don't tell a joke simply for the sake of telling a joke (at least, don't make a habit of doing that!) If you want to be humorous, do your best to make sure that the humor you share helps to drive home your point, or make it more memorable.
In addition, the Don't Waste My Time principle means that you will be well organized and prepared. For myself, there is nothing that drives me up a wall more than a speaker who keeps taking bunny trails that lead nowhere, or keeps repeating themself again and again, because they can't figure out where they are going. Because it drives me up a wall, I'm fairly careful not to do that to others.
Do: Tell Me Something That Matters
Again, this goes back to the quest for meaning. If I'm sitting and listening to a speaker talk for forty minutes about the doctrine of justification (which certainly does matter!) I don't want to just understand justification, I want to understand why it matters to me.
If I don't understand why it matters to me, then you might as well be speaking about the physical characteristics of the eighth moon orbiting Jupiter.
Do: Be Specific
How many times have I heard a speaker give some broad generality (examples: "You must love your neighbor as yourself," or "You must surrender your life 100% to Jesus!") and then moan and complain because no one is listening, no one is doing it.
The problem is not that people are unwilling to listen and obey; the problem is that they don't understand what it means from day to day. So when you speak in generalities, your audience (quite correctly) recognizes that you have given them an incomplete lesson -- you haven't told them the specifics of what that lesson means. So they are still waiting for you to finish your lesson.
Your own personal life can be a big help in being specific. As you have learned lessons in your own life, you have not truly learned them until you have discovered how they make a difference in your own life. So when you are speaking in generalities, you can move from general to specific by saying something like: "When I started to understand this lesson myself, one of the ways I began to put it into practice was..."
The simple, specific illustration or example helps your listener visualize just what you're talking about.
Don't: Berate Me
When you are teaching, you should use what I refer to as my "Optimism Principle." The Optimism Principle comes from I Corinthians 13, which says "Love hopes all things." In other words, when you are teaching, teach with an optimistic assumption -- the hope that your listeners will, when clearly shown what is right, respond appropriately.
The beraters are the ones who begin from the pessimistic assumption that the congregation will not respond appropriately.
What happens when you berate your audience? Let's take a specific example (You see? I'm following my own advice about being specific!)
In my church we always find it challenging to come up with enough workers for our children's program (AWANA). Let's say that we've got 120 people in our congregation, and our AWANA program needs ten adult leaders, and we only have seven leaders currently working in the program. This means we need three more leaders to function effectively.
Now, when I have the opportunity to ask for more volunteers, it is tempting to berate the congregation, saying, "How come you people aren't helping out?"
But remember this: the book of Ephesians says that God has fitted us all together. This means that in this congregation of 120 people, there are three people that God has groomed and prepared to step into those positions. So if I berate the congregation, I'm actually being completely unreasonable to 117 of the 120 people!
And those remaining three? Well, there's a good chance they were just waiting for the opportunity to serve, but when you berate them for not volunteering, when they didn't even know there was a need, you have turned them off, and increased the odds that they won't volunteer, just because you've implied that they aren't doing what they were supposed to be doing in the first place!
The Golden Rule
Now it is your turn. Ask yourself the question: If I was in the audience, instead of behind the podium, what would I want/expect/need? The answers you give will help form your manner of teaching.
[Added content -- June 2018: All of life is a learning process, and the following paragraphs represent lessons I had not yet learned when I delivered this seminar.]
Correcting Faulty Understanding
As you study the Word, you will, on occasion, discover things you were taught that are actually not true. It is a grave and common mistake for pastors to take verses out of context to "prove" a point they want to make, and we, as listeners, take for granted that these usages of verses are appropriate.
(Jeremiah 29:11 , for example, is a prime instance of a verse which has been popularly and inaccurately used without its surrounding context.)
When you study a passage, and discover that what you were always taught about the passage is not at all what it actually says, you will be tempted, when you preach on it, to begin by telling everyone that their understanding of this verse is incorrect, and you're going to show them the correct understanding.
However, in most cases, this is an unnecessary starting point, and telling people they are wrong, before you even begin, is a surefire way to put your congregation on the defensive, and make it harder for them to hear what you have to say. In addition, it has the added risk of coming off as smug and superior, which also leads to people closing their ears and hearts to what you say.
Instead, simply teach what the passage says, in its context. Your congregation, if their hearts are open, will draw the appropriate conclusions about what they used to believe vs. what the passage actually says, without you having to make a big deal out of it.
If you have previously taught the passage incorrectly, that's a time that it's appropriate to start off by saying, "I need to begin with an apology, because in the past I've taught this verse to you incorrectly, and I need to correct my teaching of it." This is a statement that produces no defensiveness on the part of the congregation, and demonstrates appropriate humility rather than superiority on the part of the teacher.