One thing I learned is the importance of temp control. If you dont have a thermometer, set your iron and let it warm up. Once ready, splash a couple or drops of water on the irons bottom. If the water immediately evaporates, you might be too hot. Lower temp, let iron sit and cool, then try again. For me, Ive always found the best setting to be where the water drops sit for a couple of seconds or so before evaporating. Thats a good place to start for tacking/ironing down without shrinkage.