Spread the flat sheet on top of the fitted sheet, and smooth its wrinkles with your hands. Align the top of the flat sheet with the head of the bed, and arrange the flat sheet so that it hangs evenly on all other sides of the bed.
Tuck the bottom edge of the flat sheet neatly and smoothly between the mattress and the box spring.
Stand on one side of the bed, and grasp the bottom of the flat sheet about 15 inches from the end of the bed. Hold the sheet up with one hand.
Grasp the draping end of the flat sheet with your other hand, and tuck that part of the sheet under the mattress to form a 45-degree angle at the bottom corner of the bed. Release the sheet from your first hand, and smooth that hand across the side of the mattress. Tuck the side of the flat sheet under the mattress all the way up to the head of the bed to create a secure fit.
Repeat the sheet-tucking procedure on the opposite side of the bed.