Back in 2010 I went on down to Melbourne to give a talk on iOS device sensing for /dev/world/2010 on behalf of the AUC. While it went well enough for my first public presentation, I certainly learned the lesson that you really need a lot of preparation and rehearsal before the event. Besides rambling for a good portion of the presentation, one of my biggest mistakes was trying to be fancy and making code change brightness/color when going over it to the audience. This proved to be a bad idea because the room was partially lit, and the interplay of shadows and lighting wrecked the effect I was going for.
Not bad I suppose, but I can't stand to hear myself talk.