Take something as simple as having lunch with a few friends and you want to tell them a story about something funny that happened that morning. While talking, you naturally shift your eye contact to each of your friends. You do this to make sure they are paying attention and to gauge their reactions. If the waiter comes by to check on you or someone interrupts to borrow some napkins from your table, it might cause you to pause for a few seconds but then you launch right back into your story. If it takes you a few more seconds to remember where you were in the story, you don't nervously apologize; instead, you collect your thoughts and pick up where you left off.
Next, picture a meeting with your colleagues. The boss asks you to give a brief summary of what has been happening in your department that month. You refer to a few tables and charts to be able to give the exact numbers but mainly you are looking around the room at the other department heads and the boss to see if they are following. If the boss interrupts to clarify something, you consult your notes, answer, and continue on. You know what to say because it's your department, not theirs. No one knows better than you what's been happening in your department and you have been doing this for months now, maybe even years.
If you teach, you present every day. You know when to cut an activity or discussion short because the class is about the end and the bell is going to ring. You know not to turn you back too long on the class because all hell will break loose if you don't watch the kids like a hawk. You make sure the people in the back row can hear you and write on the board with big letters so everyone can see.
However, when we have to present in a room full of our peers (and especially strangers), we forget many of these basic presentation skills. Maybe it's the change in eye level when we're standing and everyone else is sitting. Perhaps it's that we don't feel like an expert on the topic we are presenting that day. It could be that we forget what it's like to be on the other side of the room but common errors find a way to creep back into our presentations. We forget to look around the room as we are speaking. We let small pauses bother us. We stare at our notes or slides so long that we end up talking more to them than to the audience. We go over our allotted time. We use tiny font on our slides and mumble because we're nervous.
The next time you have to give a presentation, try to remember that you speak to people with the spotlight on you all the time. You were probably quite nervous the first time you had to speak at a meeting of the department heads but a year later it was no big deal. Teaching your first class nearly gave you a heart attack but now it's old hat. Presentation situations and stakes will change but it isn't all new. You've done this before so don't forget the basics.