First, before adding cardboard to your compost heap, remove any plastic tape, labels, or other inorganic materials. Then, wet your cardboard.
Add brown materials to the pile, such as dead leaves, straw, etc. Next, dampen the compost pile by sprinkling or misting it with water.
On top of your brown organic materials, place a four inch layer of green materials. Green, or nitrogen-rich materials, include fresh grass clippings, food waste, etc.