You can’t just jump into car drawing and expect results the first time. You must know first the fundamental techniques. It is mandatory to practice these as often as you can. If you skip these your progress will be very, very slow.
The first technique you must get familiar with is to draw the most basic things:
Draw circles, ellipses and lines.
What I like to do is to set a timer at about 3 minutes and sometimes 5 minutes and practice drawing each element until the time runs out and then move to the next.
All of these you should do at medium speed. If your stroke is too fast it’s harder to control and if it’s too slow it looks shaky. Draw without moving your wrist nor touching the table with your arm. Make the strokes with your shoulder, unless you’re making very short and small strokes. It sounds counterintuitive and it takes some time to get used to it but it’s the correct way.
So that’s 5 minutes each for a total of just 15 minutes, ideally, daily. That´s not a lot of time for the technique that will help you the most. Good line quality is very important.
Drawing circles and ellipses will help you draw better wheels.
Draw each circle and ellipse about ten times without stopping and then do another.
When it comes to drawing lines I place two dots about seven or eight inches from each other and then try to hit them both with a line. You can start with five inches if you want. To improve your precision draw on top of those lines a few times.
To maximize my practice time and space I try to unite every dot on the right with every dot on the left. This is actually quite messy (I told you I was) but in doesn’t matter, it´s just practice. And after I finish on one sheet of paper I turn it over and practice on the other side as well.
Draw also curved lines. This is a little bit trickier because you have to hit more dots with the same line, three or four dots most of the time. This one is actually quite hard at first. I know it was for me. As you can see I still don´t get it right every time.
When it comes to materials use whatever you feel most confident with; pencil, pen, marker, even crayons if you feel like it.
You can also use a ruler and stencils if they´re available. Try not to use them too much though, it is very important to build your free-hand abilities.