What is the FIRST thing you should do when you realize you have a flat tire while driving?

Put both hands on the steering wheel and avoid abrupt actions like hard braking.

Where should the jack be positioned on the vehicle's frame for lifting?

On the pinch weld, if the vehicle has one. Consult the owner's manual to confirm the correct jacking point.

To prevent the tire from spinning while loosening the nuts.

I can demonstrate the steps for safely changing a flat tire.

1
The first thing you should do when you realize you have a flat tire is to put both hands on the steering wheel and pull over to a safe spot.
2
Before jacking up the car, make sure to set the parking brake and hazards, and loosen the lug nuts while the tire still has some pressure on it.
3
When tightening the lug nuts, use a star pattern to ensure the wheel gets a nice even seat onto the hub of the vehicle.