Steps: First, line up your two pieces of wood together and match up the edge you want to keep. Draw a straight line across both pieces of wood closest to the opposite edge (the edge you will cut off). Using your saw, cut off the edges that will be against the wall. Using wood glue, glue the two pieces together in the middle and clamp together (this is optional, but will make the seam less noticeable and the shelf stronger). After it is dry, screw in your corner brackets, I found that the shelf was stronger when I hung it with the "L" right side up. Screw in to the wall and make sure the shelf is level.
*How Great Thou Art Print was purchased here.