So many ways, but it depends in your style and decor. Adhere shells, driftwood or baubles and old jewelry. or paint it a funky color. Check Pinerest
Do you have a photo? That could help with ideas! :)
I found several different videos on YouTube. This one I liked especially. I hope it helped...
Here is what you can do with an old mirror. I made this mirror but it is the same process https://www.homeroad.net/2016/05/repurposed-glass-door-welcome-sign.html