Here's my first study, a Volkswagen Golf Mk5. I read somewhere before that marking out the shapes with splines first can help to visualise them in 3d as blueprints are sometimes difficult to read. I'm not sure whether to model out the whole body as one piece first and then cut out the panels or just work on each piece separately. I opted to work on a piece at a time but match the edges between pieces to maintain edge flow.
This came out at 2530 tris for the body. I tried to keep a strip of edges around the main shapes like the lights and wheel arches (forgot a bit more around the arches). I think I could have continued more loops along the door to flow around the rear light area and I'm not sure I needed to cut in the rounded shape in the windscreen as that's inside the car.
Feel free to leave any feedback or tips, I'd very much appreciate it.