One of the most common rookie mistakes (that I was guilty of) in sales demonstrations is showing every operating and setup screen in software and then showing the product in action. "Look...you can do this...change that!" Don’t show and review every set-up field (especially ones that the user may never use) or you’ll scare away the prospect with the wrong impression that your product is overwhelmingly difficult to use. You want to demonstrate to the user how easy it is to use the system, the flow, what the output looks like, etc. – and then ease into the set up intricacies if necesssary. Let the user guide you as to what is important to him/her and then show what they care about. Understand your customer's "hot buttons", the problem(s) that they want to solve, and how you can solve it. (You still need to know about the steak so that you can expertly answer questions but sell the sizzle.)
If you’re a product manager, it’s always a good idea to add some sizzle into your products to help aid customer demonstrations and selling.
Another tip: don’t use jargon unless they are industry terms that the customer also shares with you. Otherwise, speak in plain English and use words that everyone can understand.