Folding fitted sheets is always trickier than folding a conventional rectangular sheet. First, throw the sheet onto the bed. Then use your hands to tuck all the corners in on themselves. Then lay the sheet back down and straighten it. It makes a horseshoe shape with its elastic. Then fold one corner over the top so that all your elastic hangs over one hand. With the other hand grab the other corner so you can lay it down flat in a half moon shape with all the elastic together in one place. Then fold it into thirds one way and then into thirds the other way.