Why do we teach in church? Why have sermons? If you don't know the purpose, then how do you know if you're accomplishing it? How will you know when you've been successful?
For many, the answer might be: The Bible commands us to do it, so we do it. That is true and important. But that's also unhelpful when it comes to evaluating how well it's being done. Maybe we could ask, "Why does the Bible call us to teach?" What is God's purpose for having teaching in His church? Some might answer: To inform and educate the people of God. But that's a circular answer. That's like saying we teach so people will be taught.
Here's my answer: We teach biblical truth so people will think and act more biblically--through the Holy Spirit for the glory of God, of course.
You know your teaching is successful when the people you teach are living differently. Put another way, we measure application, not awareness. Information is essential to growth, but not sufficient. People must translate your ideas in to specific changes in their lives (whether internal or external changes) for your teaching to be sufficient.
That doesn't mean every sermon has to be a topical, "4 steps to a better..." sermon. I'm a huge fan of exegesis sermons (where you go through a Bible passage line by line to see what we can learn). But whatever your format, your members need to have the chance to translate those biblical ideas into their lives--even if the "behavior" is better thinking. So, not only does your teaching need to at least finish in some tangible way, your people need the time to try to apply it in their lives before you dump the next big idea on them.
Are the sermons at your church more geared to be spiritually inspiring and impressive, or to help the people think through how they'll live differently in the next few days? How much time are you allowing for people to process the ideas being shared?