Remove any loose or soft skin from the onions, but do not wash them before storing them, as moisture can cause them to spoil. Store the onions in a cool, dry, and well-ventilated place, such as a pantry or cellar. You can also store onions in a mesh or wire basket, a paper bag, or a cardboard box with holes for ventilation. It is important not to store onions near potatoes or other vegetables that release moisture, as this can cause the onions to spoil faster. If you have cut onions, store them in an airtight container in the fridge and use them within a few days.