The best answer to this is literally "I don't know." I can actually observe what my hand does and give you an answer, but the truth is that I don't conciously make a choice. I do rely on the bumps on f and j to align my fingers initially, and I know I make use of keys with different shapes as landmarks. Otherwise though it just kind of floats around. I would guess it looks a bit like playing a musical instrument (but I don't play any, so hell if I know.)