An audience is more likely to listen to what you say if you project confidence in how you say it.
We perhaps misleadingly refer to a talk to an audience as a "speech." In reality, the words that are uttered are just a fraction of what an audience consumes.
Audiences watch you speak and form judgments about you based on your body language and voice intonation, as well as on your words. Some estimate an audience impression is based on 80 percent of what it sees and only 20 per cent on what it hears.
So instead of preparing a speech, prepare instead a performance.
When you give a speech or make a presentation, you may literally be on stage. Take that motif to another level and conceive of yourself as a performer on stage. Think like an actor who blends his lines with body movements and positioning.