Before attaching the cat window perch, make sure that the window is very clean. You may want to clean it multiple times with a cleaner specifically designed for glass. Put a small drop of oil on the inside of the suction cups that came with your cat window perch. Press the suction cups to the glass firmly and attach the cat perch. Most products come with helpful instructions for installation and may even include a microfiber cloth the get the glass as clean as can be.