Remember that horrible piece of advice you got right before making one of your first public appearances?
Just picture everyone in their underwear.
I was 10 the first time I heard that advice. I'm 28 now and it still makes me want to shove my head in the sand (which is what I'm sure my reaction would be to a roomful of people in their skivvies.)
No, thank you.
The meaning behind the advice is great. The purpose of picturing everyone in their underwear is not to blind you or make you go run screaming from the mic, but instead to make you feel like everyone is on the same level. When you're on stage, you feel exposed and like you're bearing all for the world to see - so the underwear trick is supposed to make you feel like everyone else is exposed too.
There are some better ways to do that than picturing yourself as the grand marshal of the no-pants parade.
Meet & Greet.
Get to know some of the people who will be attending your presentation. Show up an hour early and shake hands with the people that come in. There is no better way to feel "on the same level" than to know what you have in common with your audience.
Remember: This Isn't High School.
Since we're adults now and don't have to face an auditorium full of people who are just looking for a reason to judge you, we can let everyone keep their pants on. Everyone in that room wants to hear what the professional and grown up version of you has to say so tell the teenage you to sit down and relax - their job is done, you'll take it from here.
Open With A Story.
This is a great presentation technique over all but it's especially effective when you're trying to find some common ground with your audience. Once people can relate to you and it feels like you've bonded, you'll feel more like you're having a conversation and less like you're lecturing people.
Picturing everyone in their underwear is going to very little, if anything, to boost your confidence. How are you connecting with your audience to calm your nerves. Remember to forget the underwear (except for yours... you should remember those...)