If it helps, they say most people are more afraid of public speaking than of dying, so you're not alone :-) I would say the main thing is to be prepared. Have your remarks all worked out ahead of time. There are many websites on the Internet that give tips on how to write and deliver a good speech.
After you've prepared, the second most important thing is to just relax.
Relax, and don't be too tied to your text. 3 points: 1)Tell them what you are going to tell them, 2) then tell them, 3) tell them what you told them.
In other words, an opening, the body of your discussion and a quick review. Look up and out over the audience, then choose a face and speak to that person for just a second or two, then move on, and do it again. Pres. Obama might not be my candidate but he is a fantastic public speaker. You could learn quite a bit from watching him and how comfortable he is.
Let's see... 1. Know whatever it is you want to talk about well. 2. Really believe in what you want to say. 3. Make it come from your heart and it will change others' hearts. 4. Speak TO people, not AT them. 5. Say what you have to say and then stop without going on forever. With that last one, I'll quit!
Be passionate and an expert on your subject. Practice and follow your outline to keep it flowing. Make sure eveyone can hear you and the room is not too cold or too hot. Have frequent coffee breaks and snacks. If an all day seminar, lecture or workshop plan to end it early and you'll get return followers. Go late and past time and you might not get many listeners the second time.