i always pre-wash my backings then when they are (almost) dry i take them out- iron them - using starch for a nice wrinkle free finish- then i thread baste instead of pinning- i've never had much luck with the pin method- besides find working around-then removing them a real pain. some people like the spray basting method too- but starting with a nice wrinkle free backing is key & the best way to achieve that is a good ironing with either starch or sizing (starch gives a crisper finish than sizing)