i definitley have to be relaxed, or at least focused. Make sure that i am fully warm, and not cold, so my fingers don't slow down on me when i need them the most.
Mentally/emotionally, some negative emotions definitley helps me to play, angry and sad emotions work very well, especially for a piece by chopin. Some pieces really require a happy mood, and sometimes its very hard to get the right feeling, especially when this mood doesnt come to you very often
While playing your entire repertoire, sometimes you notice that some days, you play one piece better than others. This is because of this very fact, you have to almost switch your moods from one extreme to another sometimes, in order to achieve the right tone in your playing, sometimes that could be challenging, especially right after a very passionate piece or a very jumpy piece
I love to be very lyrical, passionate and emotional when i play...sometimes i have to remind myself that i cannot be so lyrical in some pieces, especially those pain-in-the-ass classical era pieces