A muslin or paper backdrop looks indestructible folded up on a shelf, but folding is exactly what creates the crease lines that show up under studio lighting later. Rolling instead of folding is the one rule that matters most here.
Pro tip: If a backdrop has been rolled for a while and picked up soft waves, hanging it in a steamy bathroom for ten minutes before your next shoot often relaxes the wrinkles.
Watch out: Never fold a fabric or paper backdrop for transport. Creases from folding are visible under studio lighting and are essentially permanent once set into the material.