You have one job

And that is to meet the aims of the presentation, so you better find out the criteria by which you will be evaluated, as early as possible.

Then plan to say 'the same thing' throughout. It helps your audience to understand, and it helps you deliver a clear message. The rule of threes helps you plan for an introduction, main part and conclusion, like an essay. But don't start writing long sentences before you have a chance to say it aloud.

It is about saying it, so just come out and say it! Then say it again, better. Then try another way of saying it..

You may add more keywords and subject terminology, add details and numerical facts, etc. But the way you say it will 'save' you if you freeze in front of an audience. The more practice you get speaking, the better.

Try convincing yourself, while looking in the mirror. 

You may be able to improve on your stance, your hand gestures, and your pauses for breathing (vital!).