Finish it basically
Nah, erm, well - you say you have no idea what to do next. So let's start by looking at what you've got so far
->Great atmosphere, and the basic lighting on the car's paint is perfect
->bg fits well
->Some cool little ideas for lights etc going on
So that leaves us with what you still need to do:
->Find some new rims - the ones you've got have day time reflections - not really what you want for a night scene
->Find some lights to c+p across - this will help massively with the overall realism and appearance of the chop, and save time brushing too
->Tidy up the paint around the front - you just need to make some of the lines slightly more defined and add in some body split lines
->Some mesh or intercooler etc in the vents
So really you've done the hard parts and you're close to finishing. It'll just take a couple of hours of focus to get it to a finished state
Good luck