DON'T put anything on the skin, just let it dry a couple days. Anything you put on the skin, be it salt, borax or some other substance, will serve no purpose and will have be washed off or the glue won't stick.
I had to wash some salted skins for a half hour before I could get them to stick, a big pain in the butt.
I already had them on the bow before I realized the one I got from a friend had been salted. when I noticed the glue wasn't working I had to make a mad dash to the laundry sink and get both glue and salt washed off them quickly so I could use them.
These were perfectly matched copperhead skins so saving one from being salted was my utmost priority.