If you distribute handouts at the beginning of a presentation, half of them will be paper airplanes before the presentation ends. A videotape that hasn't been rewound just before the presentation will always start playing in the middle. An audience would rather watch an empty fish tank than watch a presenter try to figure out how to use the remote control. Unless you are a qualified hypnotherapist, let no image remain on the screen for longer than 60 seconds. If you want your audience to all think the exact same thing at the exact same time, project a blurred image on the screen.
Computers sense fear.
Strive to keep the tools as transparent to the persuasion process as possible. An audience that is thinking about your cool use of special effects or your sexy presentation system is not thinking about your message. Never add sound or visual effects without good reason. Never fuss with equipment settings during a presentation. Keep equipment out of audience sightlines.