Some venues are more intimidating than others. Usually after the first couple of songs of a stage performance - and the resultant audience reaction - the lump in my throat goes away and my hands don't have the sweaty shakes anymore. However, I find that singing at a wedding or somesuch is much more daunting. There is no audience reaction until after the show is over. Once, I became so flustered that I couldn't even read the lyrics on the sheet music in front of me. I ended up inventing two entirely new verses! I found out afterward that most folks never even noticed. As to what to do about nervousness, I wish I had some good advice. I would even take a shot at neuro-linguistic programming if I thought it would help!