First of all, take the sheet and fold it in half and fit the corners into each other. Fold it in half again and fit all the corners together, ensuring that the edges are straight. Make a square out of the sheet and then fold 1/3 of the sheet towards the center. Fold the last third of the sheet towards the center then fold one-third of the sheet towards the center. Now fold the last third of the sheet towards the center. Get more details from http://www.wikihow.com/Fold-a-Fitted-Sheet and http://www.flickr.com/photos/catiecake/22238897/in/set-515142/.