They say that when people become Ordinands they begin by writing essays like sermons, once they get made deacons they begin by writing sermons like essays.
The purpose of a sermon is to shed light on the Scriptures and apply that to our lives. Without application it is just a lecture. Begin sermon preparation with prayer. Reflect on all the Scriptures before you, especially if you are preaching at a Mass, because the lectionary has not placed these here randomly before you, but they are thematically linked. I usually apply a sort-of lectio divina approach and what parts I am especially drawn to, what phrases or paets of the story stand out, raise questions are have resonance with the current situation I, we, the church and the world are facing.
If necessary I will then consult other sources, perhaps a commentary or a theologian or something on the subject. Make notes, use quotes only if it really can’t be done any other way or can’t be presented in more vivid, memorable way. Construct some good sentences which express what you want to convey and build a structure around them.
You aren’t obliged to tell jokes or begin with a funny story or a personal experience just for the sake of it; some of the best sermons I have heard just get on with it, or are deadly serious, but if there is a good story, joke or personal experience then use them.
The most important advice is that you have the whole of your ministry to explore a text fully, so don’t try and pack it in to one sermon. No-one listens for more than 10 minutes and the classic 45-minute sermon beloved by some churches are just ego trips for the preacher. Make one or two good points and then apply it. Save the other stuff for the next time this text comes round (which might be 3 years).
The key point of teaching is to get people to respond, not to your erudition but to the Scriptures, and to get them to apply it to their lives. How do I apply it to Christian living, to my role in society, to my prayers or to to my witness? End with it firmly aimed at the congregation.I hope that helps.
Based on 20 years of preaching the Gospel in Ordained Ministry.