Some people rehearse to a point where they're robotic, and they sound like they have memorized their presentation and didn't take it to the next level. Going from sounding memorized and canned to sounding natural is a lot of work.
My best advice is to not start in PowerPoint. Presentation tools force you to think through information linearly, and you really need to start by thinking of the whole instead of the individual lines.
To me, presentations are the most powerful device. You can't really name a movement that didn't start with the spoken word.
