Here is a set of display shelves I made for my wife to hang in her music studio room. The supports are tapered and the shelves and supports connect via dado notches. The unit hangs with keyhole slots routed into the back of the supports. The supports are made of red oak and the shelves are pine. The finish is Danish Oil with a coat of wax.
Order of operation is important here… cut the dadoes on the supports and the keyhole slots before cutting the tapers so that you have square reference faces. Then cut the dadoes on the supports. Then taper the supports and cut the dadoes in each shelf to be slightly undersize. Chisel out the taper on the sides of the shelf dadoes to fit. I added screws from the back through the support into each shelf.