Obviously you'll need a pair of shoes. New or old, either will do. Personally, I used a pair of old heels, but you can take any type of shoe. (If you do use a different type of shoe, let me know how it worked out in the comments!)
If you have new shoes, you can skip this next step. However, if you're planning on using old shoes, you should scrub any excess dirt off the bottom with some dish soap and an old sponge.
When you're done, they should be squeaky clean!
Next, take some painters tape and cover the sides of the shoes. This way the paint won't get all over the rest of the shoe.
Pour some nail polish into a paper bowl. I suggest using either a darker colored nail polish or a thicker one. Light colors and thin nail polishes can be used, you'll just need to apply more coats. You'll also need a paint brush to paint the shoes. Warning: this brush will be destroyed, so use one that you don't mind losing.
Now we get to the fun part: PAINTING! You might want to wear disposable gloves because when I did it, the paint was all over my fingers. But hey, maybe that's just me. Regardless of paint color or density, you will need to do multiple coats. I advise that for the final coat, your brush strokes go in a different direction than the previous coats. That way, you get a smoother finish.
Make sure the nail polish is totally dry before removing the tape and especially before wearing. I let mine dry overnight just to be sure.
Ta-da! I hope this inspired you to renovate your old shoes or improve new ones!