I say your next step should be to import one of the models we've got up here in our downloads section, and see how they've finished up the details, like the undercarriage, and the interior.
those are the areas that stick out the most at the moment.
After you get some ideas how those details are created, the next thing I'd do is to refine some of your materials, and your rendering environment. This includes taking up some texturing, and mapping some textures to your wheels, headlights, brake lights, and replacing the BMW logo in the background with a texture, instead of the low poly logo, which kinda detracts from the scene.
Next, I'd recommend either a higher shadow map size, or else using area shadows, with a decent level of quality for the shadows. The blockiness and jagged splotches created by having such a low shadow map size is killing the scene.
the lighting is too dark in some places. When all else fails, the 3-point lighting technique should never disappoint you. the first light would be the brightest, it's your key light. The darkest shadows come from it, and it should light up what you want your main scene focus to be. Then you've got a secondary light, which is placed in an area where your key light doesn't illuminate enough, and this is called the fill light. The final light is placed behind the object, and is usually used to increase the contrast of the edges, and add subtle lighting to areas that were lacking.
Hope these help. I didn't bother critiquing the modeling itself because it was your first model, and IMO, the best way to improve modeling is to just realize what could be improved (you'll usually know the areas just by comparing the renders to a reference picture), and then trying a new model, and paying more careful attention to the problem spots of the last model. At this stage at least, that's a far more effective method than trying to troubleshoot areas that may not have been modeled properly, or trying to troubleshoot using modeling tools you're not completely familiar with yet.
Have fun in your 3d adventures that are yet to come!
