Another thought from the scientific presentations I attended earlier this week: Never ignore your audience. And there are oh so many ways to accomplish this negative feat.
Take, for instance, the speaker who was so focused on his slides and pointing to them with a laser pen that he oriented his body solely toward the screen, paying no attention to fully half of his audience (including me). The screen was to his right (poorly positioned in the first place, but who knew? Clearly not the conference organizers). I was in the section of seats to his left. When he leaned on the lectern and twisted his body to talk to the slides, all I could see was the back of his head. He maintained this posture for the entirety of his presentation.
Had we encountered each other later in the hallway, I would have had no idea who he was. Why? I never saw his face as he spoke! I would have been reduced to asking him to turn around to see if I could recognize him from the back.