I would recommend checking out the Nutrition and the Traditional Foods boards.
A really good place to start is by cutting out sugar. This requires reading labels, and removing anything labeled Corn Syrup and especially High Fructose Corn Syrup as well. Removing flour is also usually effective. Generally this is referred to as removing "everything white", white flour, sugar, and white rice generally falls in there as well. Most people find this small change in their lifestyle to be pretty effective.