Lay out the duvet cover on a large, flat surface. Open the cover by unbuttoning or unzipping the side.
Place the duvet into the cover, making sure all the corners are aligned properly and there are no areas where the fabric is bunched up.
Open two packages of comforter clips so you have eight total. Attach a clip to each corner of the duvet from the inside of the duvet cover. Each clip should be clamping about 1/2 inch of fabric from the duvet on one side and 1/2 inch of fabric from the duvet cover on the other side.
Place an additional four comforter clips around the perimeter of the duvet on the inside of the cover. These clips should be located halfway between each corner, on each side of the duvet.
Re-zip or button the side of the duvet cover. Don't worry about feeling the clips while using the duvet, as they are covered with a soft foam padding.