Preparation and presentation
In the coaching of presenters and the moderating of presentations that I've done, I've noticed a distinct correlation between the amount of preparation and rehearsing a presenter does and the perceived effectiveness of the message. It's especially dramatic to hear a speaker do a dry, lifeless dress rehearsal, later to have them deliver perhaps the best presentation of an event, and to discover they had been rehearsing like crazy in the interim.
If you don't think rehearsing is worth your time and effort, consider Steve Jobs. His keynote speeches at Macworld garner world-wide attention. Mike Evangelist describes how Jobs prepares in Behind the magic curtain.