How to make elements of mini cooper (door, hood, fender, bumpers, side panel) and their transitions smooth? I'm making a mini cooper at the moment, and the modeling goes pretty ok. I model the mini cooper by using front, back, side and over view and match the mesh to these images and make elements of the car individually. But realistically these elements (door, hood, fender, bumpers, side panel) are aerodynamic and align each other. So how can I make the elements smooth (without modifying the general shape) and align them to make it look realistic, since right after modeling these elements and the transitions of the elements are not very smooth. 

What I try to do after the modeling:
Join adjacent elements, set 3d cursor in the gap between the elements, select vertices that are next to each other with respect to the gap (so transition of the elements), and scale to 0 on the axis that is normal to the gap. But I think there is a more efficient method. So how can I make the elements smooth (without modifying the general shape) and align them to make it look realistic, since right after modeling these elements and the transitions of the elements are not very smooth. :)

Without material cannot be seen directly:


But with Glossy shader it can be seen the fender and door are not aligned nicely:


And the side panel at back is not smooth:


The images with Glossy shader can be reproduced with this blend file (by using the camera's in the scene)
http://www.pasteall.org/blend/37591
I examined the screen shots, and then examined the blend file, and found immediately what the problem is. The geometry does not match across the joints in the body. I opened your blend file, combined the front fender, door, and rear fender into the same object using CTRL - J, and with the side view selected, switched into edit mode. Here is a screen shot:



Note that in the front fender, you have five segments, and in the rear fender you have seven, but in the door you only have four. To have the meshes line up on either side of the joints, you need to have exactly the same geometry on either side of the joint, so you'll need to add two more segments on the front fender, and three more on the door, and the x and z values of each pair of vertices on either side of a joint along the front and rear door edges will have to be identical, with the only difference being a small variance in the x value of the vertices in each pair. The same will be true of the joints between the fenders and the hood, and between the rear fenders and the rear door. 

If I were doing this model, I'd likely make the door, and two side fenders a single object, and when I had the whole side to my liking, go back, and add a couple of loop cuts to define the front and rear edges of the door.