The best natural face exfoliant I've ever used is a simple baking soda paste. Simply wet your face and your hands, then use about two teaspoons of baking soda to gently scrub your face. The moisture of your hands and face should be enough to turn the baking soda into a perfect paste. However, if you prefer it to be a little thinner, just add a few more drops of water to it.
Baking soda works as a great face exfoliant, without containing any large particles often found in commercial brand exfoliants that end up being too abrasive for my skin. However, keep in mind that sometimes the baking soda might sting a little if you leave it on too long, when that happens just simply rinse it off with warm water. If you still find scrubbing with baking soda too abrasive, try simply using it as a mask instead.
I use baking soda to exfoliate my face about twice a week, and afterwards my complexion is always incredibly smooth and soft, without feeling like I stripped off too many layers of skin. I even use it to exfoliate my body sometimes, or if you prefer something stronger than that for your body, consider using coffee grounds.