1. Make it interesting!
Well, this is an obvious one, but did you know, that the attention span of the audience goes down after about 10 minutes? In order to keep the audience listening to you, it might be a good idea to add something fresh, new and/or eye-opening every 10-15 minutes to your presentation. Try to have this in the back of your head while preparing the presentation and plan accordingly. You might want to add a short video clip, a shocking statistic or an emotional image or see point 2.
2. Make it interactive!
Creating interaction with the audience will make the audience part of the presentation experience and it makes them more active. Asking simple questions in the beginning loosens up the audience members a bit. Asking simple questions in the beginning can also give you the chance to assess your audience. Maybe you wanted to explain to them how to use Twitter and when asking "Who here uses Twitter?", 90% of the people raise their hands and 2 of them shout "We just relased an iPhone Twitter app!" then you still have a slight chance to avert disaster (though you should avoid this sort of mis-understanding when possible!!)
3. Make it suspenseful!
Suspense is awesome. Steve Jobs is a genius in this area. I'm always excited when he does a talk. Granted, it's partially because of the cool products, but he knows how to build up the presentation and keep people's attention. He would usually start with background information of the company and its products' success in the past and slowly build-up the talk towards the highlight (which is usually a new product or a new version of a product). Once he gets to the product, he doesn't just say what it is, but would first let the audience know about the need for a product such as this. He would explain that something like this has been missing. He might even compare other products first, stating that they still have their flaws. And once the audience is "hungry", only then would he show the product. Awesome!
4. Tell me something I don't already know!