Stick with it.
“All the great speakers were bad speakers at first.” – Ralph Waldo Emerson
The only way to get better at preaching (or public speaking) is to do it over and over and over again. In business terms, it’s called churning. Develop the product and churn it.
When it comes to preaching, it’s a never-ending process of learning what worked and what didn’t. It’s getting comfortable in front of a crowd. It’s sticking with it.