Here's a suggested structure of the speech.
1. As JG97 has said, you start with a hook. This can be something interesting, that engages the audience. It apart from what JG97 said, it could also be a story/scenario. I did mine on American gun laws, and I started with this:
"Imagine that
insert what you'll normally do in English classes. Suddenly, you hear the lockdown alarm. There is a shooter rampaging at school.
Scary right."
2. State your contention. This was mine:
"Clearly, America
needs to control their gun owners. They need stronger gun laws."
3. Your arguments.
And so forth
4. Rebuttals (if any)
5. Conclusion. Make it interesting. Don't just repeat the contention. Conclude the speech with an interesting question or statement.
Mine was:
"It is so fortunate that after the 1996 massacre, that we, as Australians said
no more to mass shootings. Don't you think America should do the same?"