Remove the mattress, crib sheet and any other bed covers from the crib to expose the built-in springs or wood slats under the mattress. Set the mattress aside.
Lay the crib skirt over the springs or wood slats so that the center of the crib skirt lies appropriately lengthwise and widthwise. Follow the manufacturer's package instructions.
Pull the crib skirt's drop panels down over the sides of the springs or slats toward the floor. Fit the skirt's open corners around the crib frame legs on the appropriate sides and ends of the crib.
Straighten and smooth the crib skirt on the surface of the springs or slats. Work around the sides and ends of the crib, adjusting the crib skirt so that the panels hang equally, with each panel measuring the same distance from the floor to the bottom crib skirt edge.
Place the crib mattress back in the crib. This holds the skirt in place.