Relentlessly practicing your demo gives you some of these for free.<p><i>Bring two of everything</i>. If something is destined to break, you increase your odds that it happens during a dry run, and <i>not</i> during the demo. Bonus points: you already know how your demo behaves when it fails. Avoid the stuttering "oh, it should have done X. This isn't working." Since you already have two of everything, keep practicing and overnight the new replacement.<p><i>Reduce the factors you can't control</i>. Since you already found a way to practice with the projector you will use, you already know how it works, and you know how your Demo looks on-screen. Take that time to make adjustments.<p><i>Get organized in advance</i>. When doing something over and over again, your natural optimization instincts will kick in. What started as three shells, four open browser windows, and a slideshow will turn into a browser window, and a backup script for running locally.<p>Also, be familiar with your format, and break these rules as needed. For instance, some demos require assistants who aren't directly running the demo, but act as third parties or perform safety checks (think robotics demos).