Heya,
As for technique to start, what Ed wrote pretty much covers it up, i however do not start with full throttle, but around 80%, although it depends on the car as well, WTCC 80%, Mini for example can bear almost full throttle, 95% or so...
Main thing is that you should not spin the wheel, and also do not stall the engine, needs practise to modulate during acceleration when and how much throttle you can apply until car gets full grip and you can push as much as you want.
Also helps if you have a clutch, not waiting in neutral for the red light going out, but in 1st gear with revving engine. If you do not have a clutch pedal you can map a button for it as well, you can reach the same effect.
and as for last, practise practise practise... what i do for it is to fire up an AI event with full grid, set AI strength to max 105%, skip qualy to start last, and then during start you can see clearly based on the gap between your car and the AI how good you did the start.
p.s.: do not expect to make better start then the AI, it is mission impossible...
i used to get around 0.3 sec before T1 braking when i make a perfect start.