Remove the trucks from your board.
Screw a bolt and nut in the front truck holes to hang the board vertically or the front and back truck holes on one side to hang it horizontally. Don't tighten the bolt all the way. The long side of the bolt should be on the grip tape side of the board, which you won't see when you hang the deck. Use the hardware from your trucks, especially if you have colorful bolts that complement the graphics.
Cut a piece of picture wire or fishing line that's at least 4 inches longer than the skateboard deck.
Wrap each end of the wire around one of the bolts and tie the wire in a knot. Tighten the bolts with the wire underneath to keep the wire in place. Leave a little bit of slack in the wire to allow the wire to hang from a picture hook or nail, but not so much slack that you can see the wire from the other side of the deck.
Hammer a nail or picture hook into the wall in the center of where you want your board to hang, leaving the nail sticking out an inch or two to accommodate the curve of the nose and tail of the deck. Use two nails for heavy boards.
Hang the board by catching the wire on the nail. The deck should appear to float on the wall.