Use freshly ground coffee (find out which coffee grinder is best here). Do not reuse coffee grounds because any moisture left in the grounds can cause this to grow mould.
If your coconut oil is hard, soften it in the microwave for 10-20 seconds. You want it to be soft but not melted. If it melts, let it harden a little bit before making the scrub.
Combine Epsom salts, coffee grounds, cinnamon, and coconut oil. Stir well.
Spoon into a mason jar.