The motion of a car is resisted by air, since the car will experience collision with air molecules, which will resist any change in their state of motion. There are few factors which affect the air resistance of a moving car. These include, shape of the car, its surface finish and velocity of the car. We tend to avoid edges when making cars and try to make them as streamlined or smooth as possible. Any abrupt edge or corner, will simply the air resistance. That is the reason, we have so many curves on the car. We also keep the car surface smooth to provide a smoother passage for air flow and hence use paints and polish. At higher speeds, more air resistance is experienced, however, it would be impractical to slow down to reduce air resistance. We can however take some steps, such as keeping windows closed, while traveling at high speeds.
The friction in a car can be reduced by using proper lubrication in various parts.
Hope this helps.