I had a friend who was just put in a church position ask me if I had any ideas about that to do about being nervous before speaking to big groups. I didn't have any real words of wisdom to cure all the jitters but I know it is a big fear for anyone (myself included). What I have are suggestions that work for me but they are just that, suggestions but they come from three years of trial and error (including my first EFY when I got so scared I almost fainted in front of the whole class).
First, when you know what topic you are to teach on I would do a little basic research early and then (with a prayer in you heart) let it sit for a day or two. Watch for examples of your topic in everyday life, with you family, husband or other people interacting. I think that sometimes the little personal stories that people can relate to can personalize a message, scripture or teaching.
Second, I know this may seem like I am preaching to the choir but as I go to write my talk, I pray to know what God would like me to teach. Sometimes I get something I KNOW should be included in a talk and other times I just hope that Heavenly Father will stop me if I am wrong. Learning to discern what is coming from God, what is coming from me, and what is coming from me trying to be God, has been one of my toughest lessons and I don't always get it right but that only means I need to listen better the next time.
Third, one of the biggest things I do is to start with something kind of funny or a story. Since those first seconds are the most terrifying, I like to start with a story I can tell easily while looking at the audience. It gets people's attention and it helps you get through the worst of the nerves. Then I would add another personal story for every 10 min or so of doctrine or scriptures. It gives people a minute to absorb what is being taught and brings attention back for people who have lost the thread of the lesson.
Finally, when it gets down to actually speaking, I never can do it without being nervous but there is comfort in knowing that I am speaking about something that is bigger than me. That despite my weaknesses, God will open the hearts of those who want to be taught. With that being said, the only practical advice to give you is the Holy Ghost is the bringer of peace. Being nervous is only a sign of your humility and that you are willing to submit to what the Lord has asked you to do. If that is what He asked, He will provide a way for you to do it. That has been promised to us. I wish I had a magic cure to make the jitters go away but the only way I can get though it is to put my trust in the ultimate Comforter and pray that your heart won't stop before you stand up.
I hope this little bit of info can help someone next time they are asked to teach or speak (particularly in church).
Paxton also adds that he finds comfort in knowing that half the people aren't listening or are asleep anyway ;)