Start with a basic salt mix of one cup Epsom salts and one cup rock salt (you can use kosher salt, sea salt or rock table salt). Most can be found in the cooking or cleaning aisle of the grocery store. Sometimes I find them at the dollar store too!
To craft a scented salt you want to use 100% natural essential oils. Avoid perfume oils or potpourri oils as these can cause an allergic reaction when they come in contact with the skin.
To condense this all down into a recipe try this:
1 cup Epsom Salts
1 cup kosher salt (or rock table salt or sea salt)
10 to 12 drops of essential oil
1 Tbls. dried herbs to match scent (optional)
Blend all items together and place in a tightly lidded jar.