Take a breath and tell yourself what a great opportunity this is. Sometimes being scared is a good thing because if you can push past the scared you have conquered a fear and for that you should be proud of yourself! Not everyone can do it it will prove how strong you really are!
I do the end of the day announcements. I just turn the mic on, take a slow, deep breath, and say it loud and clear. And just pretend you're talking to someone right in front of you, or even to yourself.