I prewash, but only yardage. Jelly rolls, layer cakes, charm packs will ravel too much if washed in a washing machine, plus the jelly rolls will wrap around each other. If a kit comes pre-cut, then, no, I don't launder it. If it's all yardage, then it's washed and dried before I use it.
I take yardage out of the dryer, fold it, mark it's measurement and then fold it up for storage.
It is ironed when I am ready to use it.