Select a decorative box that your modem will fit comfortably in with a bit of extra space for air. Cut out a rectangular slot in the back of the box the same length and height as the back of your modem for easy access to the various plugs on the back of the modem. Poke discreet holes around sides and top of the box to allow for air circulation. Place your modem into the decorative box to conceal it.
Wind up excess lengths of wire and tuck them into appropriately-sized decorative boxes. Cut small notches in the tops of the boxes to allow the cords to pass into and out of them. Stack the boxes neatly on a desk or floor as a decoration.
Move your printer and computer closer to your modem and power source to avoid excess cord from showing.