When you're giving live demos, it's always handy to have everything you need for that demo ready to go. Have powerpoint already loaded, have the application you're demo-ing already loaded, and have anything else ready to go, too. If you'll need to show a calculation, have Calculator already running. If you'll need to write some code in Visual Studio, have that already running & open to a blank project. The idea here is that your audience should never have to watch a splash screen or "Loading" dialog. Before I run a demo, I launch all the apps I need, and organize them on the Windows task bar so that they're in the order that I'll use them. Then I just click right through the task bar as I go from one activity to the next.
Additionally, if you're going to demo any feature that takes longer than 10 seconds to complete, consider having a "before & after" of that feature, where you walk through the steps needed to perform the action (the before), and then have a finished version of the feature ready to show off (the after).
(A note here - always tell your audience about how much time the operation should take to complete. You don't want to misrepresent how fast your application works, that's a sure-fire way to lose credibility in your customers' eyes. I usually say something like "This operation usually takes about 5 minutes to complete, so instead of making you stare at my hourglass for that much time, I've already got a finished sample right here")
I call this the Julia Child approach, because I was first exposed to it while watching Julia Child's cooking show back when I was a kid. Julia would have all her ingredients and utensils ready, so she'd smoothly go from one prep task to the next. For example, if she needed to chop some tomatoes, she already had the tomatoes washed, and there was a cutting board and a knife right there. You didn't need to watch her hunt around for anything, she had it ready to go. Then she'd walk you through all the steps to make a cake, then put that cake in the oven. Then she'd move over to a second oven, and remove a cake that had finished cooking. It was a great way to show both the preparation and the finished product, without needing a lot of filler in the presentation.
So having all the pieces of your demo ready to go will make the presentation go smoother, and having a "before & after" prevents awkward lapses in the presentation. All in all, this approach helps ensure a clean, smooth presentation that your customers will eat up. Bon Appetit!