Good job, Janie. And good photo. I guess my verbal description was pretty close.
Depending on how you harvested the leaves there are two ways to dry.
If you picked the leaves individually, lay them out on screening or hardware cloth in a warm place, but not in direct sunlight. As they dry, turn them periodically.
If they're still attached to branches, bundle the branches and tie them together. Don't over do it. Take a paper sack from the grocery and cut a small hole centered in the bottom. Pass the string you used to tie the bundles up through the hole so you can pull the bundles inside the bag. Then hang it. Again, warm but not in direct sunlight.
When the leaves are crispy dry pulverize them in a blender, food processor, or spice mill. Ideally, if you have the time and inclination, a mortar and pestle. You want them actually powdering to use as file.
If you rub the leaves you'll really get to appreciate their smell. Very much like root beer, because the sassafras roots are a major component of that drink.
Sasafras tea is an old-time drink, very popular with mountain folk. Because it's a mild diuretic and detoxifier, it is particulaly popular as a spring tonic.