The last general principle Cleophus LaRue writes about in his book before walking through the methods of the great preachers is Preaching Out of the Overflow
It is kind of like the movie director who must leave a lot of good scenes on the cutting room floor. You can’t preach everything you have studied. We all have probably seen the preacher who just puts stuff into his sermon becuase he studied it and wants to force it in.
But more than this, William Stidger has a metaphor of oil for preachers. He said that some preachers are dry holes, wells that have to be pumped, and overflowing wells. The great preachers only use that part that is gushing out of the well to preach from. They have a disciplined study life and pastoral sensibilities so that they always have a message from the Lord.
How do you get this overflow? You get it by disciplined study, conscientious reflection, and a connection to the Spirit.