Gather your supplies. (the list in the left sidebar)
It's a good idea to plan these out ahead of time with a 1" diameter circle template. Some images on the cards are too large to cut out into a nice photo.
Also, I bought my bottle cap keychains from a supplier. Making your own can be very easy, though. Browse around to find tutorials.
Cute the main image of the card out (the rectangle). This way your paper punch will have enough room to get to the desired spot on the card.
Line the card up with the paper punch's punch window. I recommend using a punch with a lever on it. These cards are thick, and some punches may not cut them. For example, I have a large punch where you press the entire blade down from the top. Not only is it hard and painful, it will not cut well.
For added strength, lightly sand the back of the punched out image and the center of the bottle cap. This gets rid of the slippery, shiny surface.
Glue the image to the center on the bottle cap. Press down around the entire image instead of just the center. You want a good bond all the way around the circle.
If extra glue leaks from under the image, use a tissue or toothpick to clean it away. This is where clear drying adhesives come in handy.
I used resin circle stickers to top my keychains off with. Simply peel them off the paper, line them up with the image, and press them down really well.
*Remember to pull them up from the sides to decrease fingerprints.