The two best things you can do are:
Be informed. Listen to the local weather station, check Google for weather, or check the weather on your phone. Also, allowing severe weather alerts on your phone allows you to get tornado watch messages when the weather is turning and tornado warnings when a tornado has touched down in your area. Heed warnings and seek shelter underground immediately in case of a tornado warning.
Be prepared. Keep on hand one gallon of water per person, per day, for three days. Non-perishable food items should be stored