I soak the pieces then lay them on a towel and roll the towel up to partially dry. Then I finish it up with the iron. Works like a charm.
That said, I generally only prewash if it's for a swap or if the colors are intense and I don't trust them not to run.
Of course, if I start to wash ANY part of a project, I am a firm believer in consistency and I wash all of the fabric for that project.