There's an old adage about speaking: Tell them what you are going to tell them, then tell them, then tell them what you told them. It's so often used in business presentations, it's sometimes known as the "business sandwich" Some years ago, I used to advocate it as the way a speech should be structured. I don't believe it now, and I say it is time to dump the sandwich.
Whoever came up with the structure in the first place was probably not a storyteller. That's not the way that stories work. Stories are about entertainment, interest and powerful messages that make an impact. Those are all the characteristics of great speeches too.
So what do I recommend as a structure? Here's my take on speeches:
* A stunning opening line - a controversial statement, maybe a question
* Go straight into a personal story that relates to your message
* Reinforce the point of the story, by emphasising the evidence
* Give them a practical example they can use
* Repeat steps 2-4 as necessary
* Engage with your audience as often as possible
* Summarise very briefly
* Deliver your killer closing line
* Take questions
* Deliver your killer closing line again
It sounds simple, because it is. It's not boring, because it mustn't be. One more thing. Every speech should have an unforgettable phrase, moment or story. That's what people take away, regardless of the structure.