We should not rest on our laurels. To keep recycling our own thoughts or messages is a sure way to stale, powerless speaking, and it also keeps us from learning new truths. For instance, if we are guided to give a message on the same topic as we have before, we had better be sure to put in just as much time, prayer, study and effort as we did the first time. We might come up with a message that is substantially the same, but at least it will be fresh. When we bake bread we may use the same ingredients each time, but it makes a lot of difference whether we bake all our bread one week and live off those loaves for the rest of our lives, or if we bake our bread fresh each week.
Teaching requires preparation.
A healthy, vibrant personal spiritual life is a must. Without serious Bible study on our own part, we have nothing to share with others. We ought not to expect our messages to affect those who hear any more deeply than they have affected us. In that case we ought not to be surprised if it only gets into the minds of our listeners. Teaching must be Bible-based.