The more aligned they are to one another, the better … The Traditional Method. Lay your comforter (or duvet) on top of your bed. How To Put On A Duvet Cover Step By Step. Make sure it’s laid flat and smooth. Ensure all corners and edges are aligned neatly. Take your duvet cover and flip it inside out. This will make it easier for you to put the cover on the duvet. Lay it down over your mattress so the corners are flat and loose.  X Research source Reach inside and find the top two corners of the duvet cover. Place the duvet flat on your mattress. Hold them in either hand while the duvet cover is still inside out.