Remove the cushions if possible and vacuum the crud out of the crevices. With any luck, you’ll find enough change in there to treat yourself to a trip to Starbucks. Replace the cushions.

If you have a dryer with a steam setting, fluff the drop cloth to remove any wrinkles. If not, don’t worry, the wrinkles will smooth out over time.

Drape the drop cloth loosely over the sofa, centering it as much as possible width-wise.

Line up the front edge of the drop cloth with the bottom edge of the sofa. It can be touching the floor or not, depending on your personal preference.

Smooth the drop cloth over the cushions.

Line up the bottom of the sides of the drop cloth with the bottom side edges of the sofa.

Tuck the excess into the crevices between the sides of the cushions and the arms.

Adjust the back side of the drop cloth so that the bottom of the drop cloth touches the floor.

Then tuck in the excess of the back of the sofa between the back of the seat cushions and the seat backs/cushions.

Use the tuck-in grips  to hold it all in place and keep it from getting all wonky. Note: You can also use a piece of plastic pipe cut to the size needed, or a long carboard tube like the ones that fabric stores use.