you didnt invest much time in these renderes
If you want to learn just take a look at other great car renders on forum.
there are planty little tricks how to setup your scene + lightning and then you will have to find some other camera position cos this one is boring and not showing intresting parts of car (dynamic shape, rims, tires...)
create studio inviroment and you can use HDRI images as they will give you nice reflections and realistic surranding.
just search forum for cars and look there and ask authors how they achive those results and you will be able to create much better test renderings in next 7 days
take materials from octane live (it will save u alot of time in tweaking materials and then learn how authors created them).
thats why we RESPECTS great renders cos you can see that author invest time + knowledge + time
Keep on good work and look and compare your results with others