When the fabric is washed and dried, I spray it with starch and let it dry. That way, when I iron it with steam it does not distort.
I used to iron/steam it every which way, and it would distort. Now I lay it on the board, laying the fabric's selvedeages parallel to the sides of the board and iron straight up and down and side to side. If I move the iron diagonally or in a circular motion, it will stretch/distort the fabric.