I iron the tops when they're done and if they have been folded before being put onto the long arm, I iron them again with starch.
I no longer have to iron the backing after seeing a Sharon Schamber video on it. She loaded the backing into the frame and as she loaded it she sprayed it lightly with starch. I tried it and it was amazing! I wanted to film it! The fabric was washed and had that un-ironed look. I sprayed each section as I loaded it and the wrinkles just totally disappeared, the backing tightened up, and it loaded just perfectly.