If you have clip-on earrings, you can give any of your plain shoes, whether they are heels or flats, a new look. If you don't have any clip-on earrings, ask an older relative. Vintage earrings (think 1950's and earlier) are often clip-ons. These earrings were also fashionable in the 1980's. Checking eBay is a good bet when searching for many types of vintage costume jewelry. As an owner of many pairs of vintage clip-on earrings, I can tell you that they are often painfully tight, which is not good when you want to wear them for hours, but great for holding them onto shoes.
Simply clip them on to the tops of your plainer shoes. "Plain" here simply means shoes without other adornment, embellishment, or cut outs. Try out different earrings with different shoes and see what you like best. Clipping earrings onto basic black flats adds visual interest. Crystal and rhinestone are my favorite types of clip-on earrings to add to shoes. It all depends whether you are looking for a more blingy look for evening, or a more classic look for day. Art-inspired earrings will also work. It all depends on the look you are going for.
So, make use of those clip-on earrings sitting in your (or your grandma's) jewelry box. And get a "new" pair of shoes in the process.