How often? Never, until I started uni. I've noticed that this semester I've been writing pieces rather quickly and usually well before the due date - this way I've had some time to separate myself from it and come back with a more critical eye. I've thought a few piece were finished, but in the past few weeks I've come back to them and realised they weren't - or rather, I could have done something differently. A work I just finished revising today went through considerable changes until it was finished, partly because the criteria we were given was very vague and I used the wrong mode in one section. Also, when we played through it at uni, the flautist wanted to have a more exciting line - similar to the piano part I had written, so she gave played a few variations on what I had which opened up new possibilities of what I could do.