Great work here - well done! Rather then just looking at tutorials (nothing against tutorials, I watch them all the time), but I would look at real world examples and also study traditional art and photography principles - composition, color theory, studio lighting. Really the best thing to do is practice and create a volume of work. Cars are very hard to light - have you looked at any reference materials? Find 5 car ads that you like and try to reproduce them - download a few free cars from Turbosquid and light and photograph them. Sometimes it's easier if it isn't your model since we tend to get emotionally attached to the things we create - it's hard to be "objective" when making camera and lighting choices.
Also - the physical renderer in Cinema is very good and capable, but it is lacking in real time feedback. This is where something like Octane or Redshft can really come into play - being able to light and build shaders in real time will help you get to better results faster. It also opens you up to experimentation where happy accidents can sometimes make the best images. One needn't spend a ton of money on 3rd party renderers or souped up multi GPU rigs. Corona is my preferred renderer which is actually CPU based, but offers a real time IPR for instant feedback. While it is in beta, it is currently free - so check it out.
Keep working at your 3D practice, but also look to other sources for education and inspiration.