One verse? Only one.
I've ranted before about the temptation of preachers to preach flowery sermons, give religious lectures and generally show off their speaking ability.
But if you want to know how to preach, you only need to read and heed one verse. Following this will save you a lot of money, save you a lot of aggravation, and help your congregation hear and keep the word of God.
It's Nehemiah 8.8. Here it is. Listen carefully:
"So they read in the book in the law of God distinctly, and gave the sense, and caused them to understand the reading."
3 easy steps to homiletical mastery: read the book distinctly. Give the sense -- in other words, tell them what the text is saying. Finally, cause them to understand what's written.
In a sense, the preacher's job is not to persuade the congregation. Not to make them feel guilty. Not even to make them trust in God. All of those are God's job, and His word does the job. (Hebrews 4.12: "For the word of God is quick, and powerful, and sharper than any two edged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart.")
The preacher's job is to preach. You've got enough to do, doing that. Trust God's word to work, and follow the humble examples of Ezra and the other Levites who preached that day.