2 weeks ago we had a birthday party for my grandma. It was a roast, so we were supposed to share funny stories of her, if we had one. I told a story, but it wasn't until I finished and went to hand the microphone back to my aunt that I noticed my hands were REALLY shaking.
Public speaking or singing do it to me, unless I am very comfortable with my audience. When I was in high school I could sing solos quite confidently, but when I went to college and tried out for the chorus, my voice and hands were shaking. Thank God I could still sing through it, but it was certainly not how I prefer to sound.
For speaking--I try to have a prop in my hand, be it notecards, a laser pointer, chalk (when teaching a lesson), or to unleash myself from the podium and meander around the stage/front of the room.
For singing--I just don't look at anyone else, and envision myself singing the song back in my high school chorus room or church.
ETA: I met my husband on CatholicSingles.com, and the first time we met in person, after about a month of phone calls and emails, I hugged him and (he told me a few months later) I was shaking.