The frame above your window or door is called the architrave. Mount your brackets on the architrave in a straight and level horizontal line. The simplest way to make sure your brackets are level with each other is to check if your architrave is level. If it is, then mount your brackets flush with the top of the architrave. It if isn't, use your level to draw a straight, horizontal line across your architrave and mount your brackets along that line. To mount your brackets, pre-drill holes for the screws and screw the brackets into place.