How to get perfect launch in NFS:MW?

At the moment of race start the pointer of the rev counter must be blue. Just give some power before starting to see where the pointer turns blue to get a feel of how much power you must give.

The blue zone changes from car to car, afaik, so you'll need to adapt.

Just accelerate the car and leave acceleration when the second countdown reaches to mid-point of your screen, and then accelerate twice...