I don't do anything but you can preshrink it if you want to. I happen to like the crinkly look of washed quilts but I can't really tell the difference when it's all done and washed. Here is one made with prewashed fabric (and washed after it's been pieced and quilted)
and a close-up:
and one made with unwashed fabric (precuts) which was washed after it was pieced and quilted:
and a closeup (the label but you can see the quilt behind it)
I honestly don't see that much of a difference. I wash in hot water and dry in a hot dryer. I figure that way whoever washes it later will be able to wash it whichever way they need to.