When drawing cars start with good reference materials, pay close attention to perspective and focus on creating the form. It may take several sketches and a lot of time to draw a very highly detailed automobile.
To create accurate and compelling drawings of vehicles, artists need an understanding of structural or technical drawing. Cars are very precise, three dimensional objects and the viewer will instinctively know when the perspective is off.
Artists, especially beginners, should start with plenty of reference materials. Draw cars from books and from real life. A vehicle doesn't have to be cool or expensive to make an interesting drawing. Artists can practice drawing their own cars or go out and look for an interesting rusted out vehicle or collection of cars in varying styles.
Start by sketching out the rectangle or diamond that forms the car's perspective lines. All the lines of the car can be built up from this square, kind of like starting from the chassis up. Focus on building up the form of the car with sketch lines. Every car has a different style from boxy to low and sleek.
As with other types of drawings, start sketching with the hardest "H" pencils first to create light lines. Then, darken lines and fill in the car with the softer "B" pencil leads.