On the day of a concert, I usually warm up as usual in the morning. Then I might play slowly through any difficult passages from the music for that concert.
In general I try to keep the day stress free, and my mind calm.
For an evening concert, I try to leave the afternoon open. I often take a nap to be sure I am fresh for the concert. Then I might take a walk if the weather permits, or, if not, I do some yoga at home.
I usually feel nervous throughout the afternoon, a pit in my stomach, sometimes a bit of nausea.
I eat a very light meal before a concert, since heavy food will make me feel sluggish. Tonight I had several oranges and some cheese. That's it. Of course, I'm usually famished after the concert.
I'm off to play a concert with the Columbus Symphony. Ciao!