Aside from the relatively recent influx of zombies, there is nothing more universally frightening than having to give a speech. Common wisdom says if you can picture your audience in their scanties, this will make the experience a lot less scary and possibly even enjoyable. (Note: The same can not be said for zombies, in their underwear, shambling up to your house; in that case, best to simply hightail it out of there.)
Back to speechifying: common wisdom is a moron. A room full of underpants-clad folk, leaning forward in their folding chairs and eagerly waiting for overdressed me to enlighten them on some topic or another... hell, that's a recipe for stuttering, lisping, senior moments and myriad other indicators of not being able to pay 100% attention to the task at hand. I can't speak, don't ask me.
Here's what you do instead.
1. Understand that they want you to be good, to succeed at this. They want this so much that they are willing to cut you all kinds of slack. They're going to do a lot of the "success" part for you, by way of justifying their presence and possibly the price of admission to others after the fact. Others who were not there. People your audience can lord it over because they were. You're going to have to get up pretty early in the morning to screw this up, believe me. But there's always an outside possibility, so what you want to do is
2. Really know your stuff. Give them something in exchange, you know? Prepare, practice, but don't read it. Say it. Write it all out first, fine, but then
3. Make an outline that is not just a diagram of the exact sentences in your written version. Then practice from the outline till you can say it all in the time allotted while making sure to
4. Smile. there have to be other things to be happy about besides a group of half-naked people sitting and watching you, but if you have to resort to that, OK, fine, imagine your audience in their underwear.
5. Ya happy?