I´ve used a couple of pieces of black vinil cut to 10x27 mm. Any other kind of adhesive tape will work, but it needs to be a smooth surface and resistant.
Cut them with a paper cutter so you get good angles and edges.
Clean the back of the display before sticking them and use tweezers to avoid your fingers grease in the adhesive.
Start attaching the stickers from the edge of the display, just next to the depression and align the stickers to the lines printed on the back of the display.
Avoid bubbles by pushing the sticker slowly toward the camera and volume buttons.
These two stickers will also help keeping the display in the open or close position. When they get too scratched or something, you can exchange them.