Well, the first thing I would tell you is to set up mirror modifier on a plane, this way you only have to mode half the car.
All so you need to make sure your blue prints are all scaled to the same size, this can be a challenge exspecial with hand draw blue prints( witch is all I can seem to find.
here is a good place for hand drawn blue prints http://www.the-blueprints.com/index.php?blueprints/cars/lotus/
To make sure the images are the same scale ratio, I usually scale a cube to go from bumper to bumper, and bottom of the wheel to the roof.
this is a trial and error exercise, so you just have to work at it, even if you get it perfect,
you will no doubt find (in the middle of modeling) the proportions are out of wack, in this case decide witch image you need to scale up or down and you can change the size of the image while you work on the particular area.
this is a great set of modeling tutorials that show how to set up a mirror mod, and how to use edge loops, you must know how to use edge loops,
Also here is my first car model, I have only been using blender for 4 months, and this is my first real render.
and the youtude animation