Well, I have been working with a teacher for a couple of years now, and she has had me working on 2 or 3 pieces at one time, with one of them as sort of a major piece. The pieces are in different periods - which makes it more interesting and so far it seems to work. It's also good if one piece is just getting started, while another is in progress - like memorizing or metronome work, and another polishing up. It's a bummer, but I am in the beginning progress of mine right now. I'ts only disappointing because there's nothing I can just "play" of the pieces I am working on - they are still too new. I am actually working on 4 right now, which my teacher would think is "too much" . - my current set of pieces, as an example, is: Chopin Ballade #1, Mozart Sonata K576, and Prokofiev's Suggestion Diabolique. I just finished Beethoven's Appassionata and a Chopin Nocturne, for example.