The people who live in the regions prepare for tornadoes by enforcing tonado sirens, just incase of a tornado touching the ground people wuld know to seek shelter.
People would normally make a plan, and where to seek shlter incase of a tornado touching the ground. That means, they make a plan of where to go inside the house.
People may also stalk up to flashlights and other supplies. After a tornado, power may be out for a while. Even if the house isn't damaged, it's best to have food and supplies handly. In many cases, tornadoes nock down tree's and power lines into the road so no one might be able to leave their house for sometime. If the house is damaged, keeping food handy is still a good way to prepare.
Those are just some of the few thing's people do to prepare for a tornado before one actually makes landfall.