I steam, including pumping lots of steam into my yardage before I cut--so any shrinkage happens then. I am careful to press, not iron, and when I have any bias edges on my blocks,I will use either Best Press, or more often actual spray starch.
as a Long Armer for others, if they haven't gotten nice flat seams when they are putting their blocks together, there is no way that I can quilt it and it will be a flat seam, there's a little tuck (which usually won't show, but you might be able to run your finger nails along it and feel it). I recently had a friend use another quilter and she complained about this, I explained to her that the seam was not flat in the block, so there's nothing the LA can do to make it flat. Make sense?