Hi this is just from my experience, but I think you should definitely ask your teacher (or whoever is marking) what they think a good speech sounds/looks like. I think speeches are even more subjective than essays and creative writing when it comes to writing, as I've had wildly different experiences with public speaking through my years. Some teachers don't mind if you would like to spice it up with comedy and more colloquial terms while others most definitely prefer you to take a more serious approach. My teacher has very firmly stated he doesn't just want it to be a spoken essay and insists we extend ourselves.
I think the most important thing in a speech though is making sure you speak confidently when you're putting forward your thesis and linking ideas. If you're convinced you're correct, your marker is more inclined to think so as well. When trying to convince your audience of something, I'd also use inclusive language (us, our, etc..) and if you're particularly nervous about public speaking, treat it as a performance. Body language is key and don't be afraid to use gestures. (But make sure if you use movement in your speech to have already orchestrated each step or sway. Teachers can always tell when you haven't planned a step or not, especially if they double as a drama teacher like mine.)
Hope I managed to help you at least a little! My own speaking assessment is coming up in less than a week and I'm endeavouring to memorise mine to give myself more room to move. Good luck though and I hope you get a good mark!