Tie a sturdy knot in one end of the rope. A loop knot works well, but any large knot will work. Call the top end rail "A" and the bottom end rail "B." The left side rail will be "C" and the right side rail "D." Number the holes left to right on the end rails, and top to bottom on the side rails.
Thread the unknotted end of the rope through hole 1A and stretch it along the bed to hole 1B. Pull the rope taut and insert it into hole 2B, then up the bed into hole 2A. Repeat until you reach the last hole on the end rails. Pull the rope very taut and tie a sturdy knot as close as you can to the end rail.
Tie a sturdy knot in the end of another length of rope and insert the other end into hole 1C on the left side rail. Weave the rope under and over the lengths of rope already laced between the end rails, then into hole 1D on the other side rail. Stretch the rope over to hole 2D, through 2D and then weave it back across the bed in the opposite pattern to the first and into 2C.
Repeat on all the holes in the side rails then pull the rope very taut and tie a sturdy knot as close as you can to the last hole on the side rails.