So the first thing is the concept of the "artistic vision." You need to think of what the piece is going to sound like. For Mompou, Música callada X, I can think of it as swimming through molasses, or as a child's music box. I have to have an overall interpretation, and also a way of directing each phrase toward that aim. People say that Western classical notation doesn't work for jazz. Fair enough, but the notation only gets you so far in classical music. You have to know how you want it to sound.
Being a literary guy, I use words to describe what I want the music to sound like. I may not achieve that, but if I don't have a conception of what it is supposed to be, then what will I achieve?
So I need to listen to what it sounds like. I need to record myself but also listen each time I play. My choir director says, "Listen harder than you sing." Every musician knows that listening is more important than producing the sound.
The piano has dynamics. Piano means soft, so the dynamics really means being able to play as soft as possible (Feldman). Loudness is pretty easy. Pianissimo playing is not weak, it still has an assertiveness to it. My concept of voicing was what notes to play (in jazz), but in classical playing it is what note within the chord to bring out. Obviously the melody note on top, usually.
Then phrasing. Bringing out the linear dimension and the structural elements.