Sewing a snug-fitting duvet cover will help keep it from sliding around, but this simple trick will ensure the duvet stays put. Before you turn the duvet cover right side out, cut two 10-12 inch lengths of narrow grosgrain or cotton webbing. Fold them in half, and stitch them into the upper corners of the duvet cover so the ends hang free.
Place the duvet on the inside-out duvet cover, lining up edges. Grab a duvet corner, and use the ribbon to tie it into place. This leaves a small tuft of duvet poking up, but it won't show by the time you're done. Do the same thing with the other corner.
Flip the duvet cover right side out, with the duvet inside. Straighten the comforter, so it fits snugly inside. Don't worry if a little sticks out the end. It's time to move on to the finishing details...
