The french cleat method is a simple way to hang really anything you want. I started with a piece of plywood 1/2 inch thick, 4 feet long and 2.5 inches wide.
Use a measuring tape to mark the same distance along the item you are hanging, and screw one of the half pieces on to it. Be sure the angle part is facing down.
Set the item you are hanging against the wall. Gently slide the item down until the boards meet, and if you did everything right you will have a straight well hung item on your wall.