Depends on what you want really. If you want to make the renders better/more different from this standard scene, and want to invest time into it, it's basically a matter of learning how to create materials and improve the lighting. Can't really tell you how to do it, because it's basically just a matter of experimenting and googling around.
The wheel material for instance looks nothing like that of a real wheel. And the totally white background and lighting make it really bright imo.
Create a material containing a texture for the numberplate and apply it to the faces of the numberplate. The standard texture is in lfs\data\dds. Can't remember what it's called but it's just a white texture with S2 on it or something.
I'd agree with joen though, I don't like renders of cars in an infinite white room. Much like I hate photos of real cars which are then edited into a perfectly white room. A photo isn't just about the car, it should be set in some nice scenery. In your case, model a garage or something and put the cars in that. A lot of work but can be re-used.