as i haven't been performing regularly, i am just going to say what i used to do. basically, get into a 'meditative' mode and focus a lot on what i want to express to the audience. it used to be very particular ideas - and as i've gotten older - more generalized. i would like the audience to be able to appreciate my playing in as many interpretations and ways as possible.
i'd like to hear responses like - genuine feeling, composer's intent was regarded, beautiful tone, flowed like a good story (had definate catchy beginning, good development, and flashy or calm ending depending on type). control is something i am always after. maybe i'm a little too obsessive/compulsive - but i want to be a performer that has control of the sound - and doesn't just 'let it happen.'
i want to know ahead of time in my mind what sound i want from the piano. then, i want to make that sound that i hear. would be very frustrated as a performer if i wasn't able to perfect this. it's like re-painting a painting that turned out well in practice.