The method you use to press your quilting pieces really does matter, and we probably have all heard this before, Press with up and down motion and not slide across your piece, but here's something else I found that really works for me that I learned from "Sally Collins teaches you precison piecing", and that is "cooling in place". After pressing quickly place something heavy ( a stack of books for example or a clamper" on your piece and let it cool..takes only a few seconds..You can use your hands but if your iron is anything like mine that piece is hot to touch! I use my old vintage cast iron , iron. although it's probably too heavy at 8 lbs. it does the trick. My pieces are flat and stay that way! This is really good when you want one seam going one way and antoher in the opposite direction. While one piece is cooling , press another ! Give it a try!