Measure the width of your window glass. Decide on how far apart you wish your hooks to be by finding an easily divisible number in your window width. If the window is 36 inches wide, you can put hooks every 3 or 6 inches.
Spray the back of a suction cup and push the cup to the window glass in the upper left corner. Spray the back of another suction cup and press it to the glass, keeping the cup against the upper edge of the glass and placing it as far down the glass width as you have calculated in Step 1. Continue placing suction cups in this manner until you have the window top filled.
Measure the width of your curtain or hemmed cotton panel. Divide this number by the number of hooks that you have hanging in your window. This will tell you how far apart to put your curtain rings on the curtain.
Sew a curtain ring to the top of the panel at the upper-left corner in the curtain. Sew another ring at the upper-right corner in the top of the panel. Sew the rest of the rings by measuring along the top of the panel the distance you have calculated in Step 3, and then sewing a ring. Repeat this step until all of the rings are sewn onto the panel.
Loop the upper-left curtain ring onto the upper-left suction-cup hook. Loop the upper-right curtain ring onto the upper-right suction-cup hook. Continue looping the curtain rings onto the corresponding hooks until all of the rings are hung and the curtain hangs evenly.