Select the frame that you'd like to hang your stamp in. Technically you can select any size frame you like, but with stamps the best frames are the ones around 5 inches or so in a square shape. This way the stamp won't get lost in the frame.
Turn the frame over and measure the length and width of the inner frame. Purchase a piece of precut, acid-free mat board of the same dimensions as the frame, in a color that matches or contrasts with the frame. Ideally, the mat board should be in a color that contrasts to the colors of the stamp, so the stamp stands out.
Use your measuring tape to determine the exact center of the mat board. Lightly mark the center spot with a piece of chalk.
Insert the stamp into a self-adhesive clear sleeve. Peel off the backing, exposing the sticky back.
Press the sticky back of the stamp sleeve onto your chalk mark. Press the mat board face down onto the back of the frame. Insert the frame backing on top. Your stamp is now ready for wall mounting.