Here's a fun craft I recently did with my Teen Art Club. We made diamond ornaments using cardstock and the template below. I used this template here. After some trial and error I decided it was easier to print the template directly on some thicker cardstock.
The teens thought it would be fun to add glitter to the diamonds-I agreed. We used Elmer's glue and applied thin layers to small sections at a time adding glitter as we went. The paper warped slightly, but the dried stiff. It's very important to use a SMALL amount of glue. Mod Podge would work to, but I only have a matte finish and didn't want to lose the sparkle of the glitter.
Here's what the glued together diamond looks like before glitter.
And here's the glittered out diamond! If you want to make this into an ornament poke a small whole into the top of the diamond and slip thread or thin fish line into it and tape secure on the underside. Glue your diamond shut with the string hanging out of the top.