If your car is absolute stock I can suggest some things I did to mine
From cheap/easy to expensive:
-Change out those stupid orange front-side lights with white/blue ones and make the mains Xenon lights - easy
-K&N panel air filter - dead easy
-Tint windows - easy
-Full kit exhaust to make it sound like a real skyline - harder
-New 18" rims - harder (need to research)
Have fun! and pls.....don't tag it..keep it simple...it's a 4 door.