Rinse off the disc with water to remove any dust and grit. Locate the scratches.
Use toothpaste as a mild abrasive to polish out the scratches. Rub a small amount of toothpaste on the disc with a clean cloth in a straight line from the center to the edges. Plain toothpaste works better. Do not use toothpaste with abrasive particles, such as baking soda. The disc may look worse, but it should be playable.
Rinse the toothpaste off the disc, and let it dry. Test the disc to see if it works. If it does not, repeat the process.