Stay away from White sugar, Dairy, White flour products which include white rice, white pasta, white potatoes, white bread.
Stick to only PURE Whole Wheat products (or spelt etc.)
It will do wonders to your skin and you will have a side benefit of losing some weight (if needed). My friend tried it and it did wonders for her skin. It may be difficult to keep up with this way of eating ,but give it a try.