Holy Cow after being away from performing anywhere for nearly 20 years I was incredibly nervous ... wow .. I asked the same question about 4 years ago. It gets better for sure. Now I just smile and relax and play but boy do I understand where you come from. YOU just don't want to disappoint anyone, so you worry about it and that worry affects your performance. What does work is knowing the songs that you play so well that it is like breathing, then say to yourself. I am playing for me ... just me .. cause I love this song ... then people will get a personal and moving experience because you are playing from your heart. visualize you sitting alone on your couch, playing a song you love ... it works for me