Jan's advice is very important because we do have a tendency to use the side of the iron and treat our pieced work like a laundry item. Treat it gently and keep the elements square. It is important to press with the straight grain. If pressing seams open, it is important to finger press them first so that you don't press in pleats and distortions. When you have the intersection of several seams (like 8-pointed stars) a clapper or wooden mallet is helpful to flatten that intersection.