It looks like you’ve set a high level of Subsurf and not smoothed it. Level 2 or 3 will do, and set smooth will hide the sharp edges of the faces.
Headlights are difficult - the best thing to do is find some really good reference pictures of them (any angle) and try and model every detail. If you skip things they may appear bland and fake.
Windows depend on if you plan to do an interior - if you don’t, set them to black and give it a bit of raymirror. If you do, make sure the glass has thickness (the Solidify Selection script is awesome for taking a zero-thickness (like a plane) mesh and giving it depth) and give it a material with VERY LOW alpha (0.05 or similar), a white or 50% grey colour, high reflectivity, RayTransp with an IOR of 1.5, and a little raymirror.
Your car currently looks like a sort of blue plastic. If you want to look professional (and spot mesh problems easier) a clay material would work well until you’ve finished modeling. If you just want a nice car paint material for the WIP renders, give it a sharp spec highlight and some raymirror with a bit of fresnel. BTW if you use any raymirror, you have to have something to reflect, so set up an HDRi map for that.
Don’t forget that a car body isn’t just a single piece of moulded steel. It’s broken up into panels, and you need to model each one. Extrude the edges of the panels into the centre of the car a little way, so that you can’t see through the gaps and look at the other side.
I might come up with some more stuff later, but its a nice start, keep at it.
Thanks for the reply, it is my very first piece of work and some of the rendering techniques you’re talking about baffle me, maybe i should have done a bit more research before commiting myself. I’ll look into a HDRi map and try and find out how to make/use one