Bay windows are some of the most challenging to decorate. If it is just the window that is the Bay then I would look to do something on the outside of the window. Typically you could add a pair of draperies on either side of the window and a valance across the top. Some customers are looking for just a valance as can been seen below. If the whole wall has been cut out to be the bay then you can design something that will have to be cut to the angles of the bay. Once finished they are a real eye pleaser.