It's different for everybody!
Some things that make my skin worse:
Washing my face with anything but cold water
Lack of good fats, especially saturated
Dairy, which simultaneously can cause constipation, which also worsens any acne - a dastardly duo!
Some things that make my skin clearer:
Freshly dug dandelion tea
Bacon, tallow, other good sources of animal fat
Only washing my face/showering when necessary, like once every three days or if I get really dirty
Steak, eggs, potatoes - fruits, nuts, berries and forage. Coconut milk and potent herbs and spices. Tea instead of coffee now and teeny amounts of kelp daily. Let's see how this does! Not really had dairy much, and gut seems better for it.