Which of the following should be done first when changing a flat tire?

When changing a flat tire, the first step is to loosen the lug nuts. This is crucial because lug nuts can be tightly secured to the wheel, and attempting to loosen them after the vehicle is elevated can lead to instability and increase the difficulty of the process. By loosening the lug nuts while the vehicle is still on the ground, you can apply your full weight and leverage to loosen them effectively.

Once the lug nuts are loosened, the next steps can be carried out safely, such as raising the vehicle with a jack, removing the flat tire, and finally placing the spare tire on the vehicle. Each of these steps depends on having already loosened the lug nuts to ensure a smooth and safe tire change.