Measure the length and width of your bed. Cut your material of choice to 2.5 times the length of the bed and 2 inches longer than the width.
Lay the material facedown on a flat surface. Pin the edges inward 1 inch, creating a 1-inch hem all around. Pin the hem in place. Sew the hem by hand or with a sewing machine, creating a simple running stitch. Remove the pins as you sew.
Find the exact middle point of the wall that your bed rests against and measure 4 feet above this point, marking it with a piece of chalk. For example, if the head of your bed rests against the wall, measure there. If one of the long sides of your bed rests against the wall, measure there.
Screw in an 18-inch metal rod into the wall where your chalk mark is. Hang the material evenly over the rod, creating a nicely draped canopy over your bed.