Suppose you are in a car and it is raining heavily with thunderstorms. Then what is the best way to protect yourself from a possible thunder strike?

The best way to protect oneself from a possible thunder-strike is to remain in the car with the doors and windows closed. The car touches the earth through the rubber tires which are insulators. So, the thunder is not attracted by the car as it does not liberate any charge in the air due to the insulated connection to the earth.