Do you want to be a better preacher? Do you want to improve? What do you do?
Consider a man who has a car. It doesn't run well. If he slaps a fresh coat of paint on it, will it be a better car? If he changes the interior, reupholsters, will it be a better car? If he adds a kickin' stereo, maybe even some hydraulics, it might look cooler, but will it be a better car? No. He needs to tend to the engine.
If you want to be a better preacher you might throw on some witty turns of phrase, you might get some fresh, heart warming stories to tell, you might even get some new sermon structures, forms and patterns that will seem new and interesting. You may even (in most of your cases - "God Forbid" - because I know what Lutherans are like) try to be hip and cool and connect that way.
But none of this really makes your preaching better.
What drives a sermon? Law and Gospel.
Want a better sermon. Be more blunt in your Law. Be honest about how often Christians sin - be honest about how this world is fallen and broken even though we try to pretend we are all Ozzie and Harriet, all Ward and June.
And of course - use this Law to sharpen a greater and greater focus upon Christ Jesus and His redemption, His forgiveness, His rescue.
The more one proclaims Christ Jesus as Savior, the better the preaching. He is the engine which drives everything. God grant that I learn this more and more.