Choose the color or colors you want to use, the keys you want to paint and pin the pin or needle(i wouldn't recommend it as it would be very thin) to the eraser
You can use tape so that you can paint carelessly. I didn't use it, but it is an option
Paint one side of the key, and you can either let it dry, to leave it like that or to paint a pattern on it(go to step 5). Or you can put glitter all over the painted part before the polish dries out.
Paint the other side. Put the key in the glitter and let the nail polish dry, after 5-10min, cover the glitter with a top coat/clear polish. (Skip to step 7).
Use the pin to paint your desired pattern. And i would recommend to paint a top coat of clear polish so that it lasts longer. And then do the same with the other side, after this one dries.
This is how mine turned out. It's a cool and easy way to decorate the boring keys and even a cuter way to ask your partner to live with you.