Raymond Sutherland wrote:
If my audience of one or more leave the room, I find that I immediately regain composure.
When someone puts me on the spot and asks me to play I'm nervous but plow thorugh especially if I go for a difficult piece. Mistakes are here and there but overall it's at least ok.
Now if I'm playing like no one is listening I do much better and it's all very automatic. There's a balance you have to find between letting yourself go and controlling your playing.
I'm no professional but I sound the best at 3am after practicing for multiple hours and when I'm tired. I try to simulate that by practicing a lot before I perform. I make it so I'm feeling tired which calms me down. Then when I go to perform I pretend no one is really listening and they are just there. The nerves will want to speed up so I'll play a little slower to maintain control (from Perf de Castro interview at classical guitar blog). Also at the performance I don't care about my mistakes, probably because I'm too tired too. As an amatuer this is what I do on day of the show that works for me. This is what I did for my volunteer performance with grade school kids. This is what I'll do when I play for the local guitar society. I'm an amatuer so I think that also takes some of the edge off no matter how demanding a piece may be.
So when do you sound the best?
What were you doing a couple hours leading up to it?
Hopefully you can simulate it hours before the perfromance and at the show pretend people are just there and play a little slower to maintain control.