Great speakers rarely take their eyes off the audience. While poor speakers read their speeches like essays, outstanding ones have learned that in order to remain relevant and engaging to an audience, there needs to be maximum eye contact between the guy standing behind the lectern, and everyone sitting in front of it.
This goes for turning your back to the audience, which should also be imprinted on your brain as a giant NO-NO. The surest way to determine whether someone is delivering his very first speech, or has never bother to get feedback on his performance, is if he turns his back to the audience and reads from his slides.
When I was involved with, and teaching theatre to University students I always wished I had a paintball gun to target young actors who turn their back to the audience. It should simply never happen and pro's know this.
So, the solution for public speakers?
It's called the confidence monitor and it's a stunning tool, though not every venue that you speak at might have one (there is a solution to that though, more below).
Why do I need it?
Because, as explained above, you never want to turn your back to the audience. This monitor is your private little way of ensuring that the audience is quite literally on the same page as you and, if you're using a presenter feature which shows you up-and-coming slides, it automatically helps you maintain your rhythm since your not forced to peek over your shoulder for your next queue.
With a remote control, you, the speaker, can now be nearly anywhere on stage and advance your slides with perfect voice-over transition.
Microsoft's PowerPoint presentation software even has an integrated notes section in it's presenter view, which means, if you have a confidence monitor somewhere, you don't even need paper notes anymore!
What if I don't have one?
A confidence monitor is not the kind of thing you want to personally buy and log around to every speaking engagement. That'll be totally unpractical. Instead, speakers are usually at the mercy of the venue with this one. Most larger and more sophisticated speaking venues will have one or two confidence monitors installed, but If you're speaking in the local high school gym, don't expect one.
There is a solution in that you can, if the venue's infrastructure will allow it, use your own laptop. With lengthy cables, and hopefully a smart and clued up technical assistant, many speakers use their own laptops and place it on their lecterns or somewhere within eyesight, and let it serve as a confidence monitor.