This is a tip I learned from Qnn yesterday. It really helped me. After you sew two pieces together, before you iron take your fingernail and run it down the seam, then press. I couldn't believe it when I tried it
In the past when I pressed sometimes one piece would move to the side, but when you do this it presses flat as a pancake.
Maybe you all knew about this, but in case someone doesn't, try it you'll like it.