You might be accustomed to cleaning up after smelly dogs and messy eaters, but uncommon stains like nail polish can really throw a wrench in your routine cleaning. Whether you're dealing with a fresh spill or an old nail polish stain, you can erase the evidence completely by following a few simple steps. Your first move should be to remove any excess polish. You can use a damp paper towel to blot and lift most of the nail polish before it dries, but be cautious not to use too much pressure to avoid working the polish deeper into the carpet fibers. After you've cleaned up a majority of the spill, take into account the color of your carpeting before using a solvent.
If you have neutral or light-colored carpet, using a non-acetone, clear nail polish remover is the best option. Before you try to remove the stain, test the solvent on a small out-of-the-way patch of carpeting to make sure it won't irreversibly damage the carpet. Apply a small amount of the nail polish remover to a cloth or sponge and gently blot until the color is gone. When the stain becomes barely visible, keep the area wet and use a stiff-bristle brush like a nail brush or toothbrush to scrub the area clean.
If your carpeting is darker in color, nail polish remover will damage the fibers and discolor the area, so you'll need to use a different solvent. Window cleaner, hairspray, rubbing alcohol and hydrogen peroxide will all remove the stain. Apply or spray one of the aforementioned solvents on to the stain and let it sit for a minute or until the area is fully saturated. Then, use a damp paper towel to dab the area until the stain is gone.
With all stains, if the solvent you decide to use leaves an unpleasant smell, you can always finish the job with a detergent and water mixture.