Drawing cars is like expericening the car as it was suitable infront of you. To me drawing a car typically provides me more insight in the particulars around the car that I would commonly not notice from just looking at a image. Get a lot more data about coloring books of the cars
Is it seriously so tough to do a good Ferrari sketch or nice Porsche drawing for that matter? That's a query I get a lot. My answer is that only patience can make a superb drawing. Since if you're not prepared to devote several hours just having the proportions with the sketch suitable, the shading right or the lights proper the outcome will probably be not quite impressive.
My best advise on how you can improve your car drawings is simply to commit much more time on them. For instance if you're not fully satisfied with the front lights, don't just continue with the drawing and hoping that the lights will get improved by some magical touch! No, look at the lights and do not give up on them until you might be completely happy with them, then move on for the next portion with the car drawing.
A different advise will be to not have the attitude of finishing the drawing / sketch tonight, because this can just make you ruch the whole drawing and get you frustrated that it really is taking longer than you anticipated.
Alternatively work an hour here and an hour there and sooner than you assume you'll have completed an excellent drawing of that favourite Porsche of yours!