For me, practicing to an empty room is actually harder than presenting. Previously, I've clicked through the presentation repeatedly, thinking through the words each time and examining the flow, but my last presentation was to a larger audience so I practiced it aloud around 3 times prior to the presentation. That made the presentation itself a lot easier and all I had to worry about was getting into the steam of things.
Practicing also helps me identify what can go wrong. I intentionally presented with no internet connection, just so there were fewer sources for unplanned interruptions. Additionally, during one of my practice runs PowerPoint crashed and I had to practice getting it back online and restarting the presentation.
I've done only a few demos thus far, and next time I do one I'm going to be sure I have pre-recorded video available on device, on USB, and in the cloud in case of catastrophic failure.
I've not had the confidence yet to try live-coding. I may never do it as I think that the benefits it offers can largely be created via slides done in a careful way.
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