You need to shift at the right time. Use your nitrous in the very beggining of the race. But be careful because once you use nitrous in the beggining, you need to react fast to shift.
Also, watch out for traffic.
The game is not too hard in the beggining. Wait until you encounter this girl racer named Kamikazi, that is where the real challenge begins. I cant beat her. Good luck on the game!!