Does this seem impossible? Don't worry about it when you start the game. I don't think it's even possible to get all the stars right away. Wait till you level up and then it will be much easier. I got this achievement when I got to the OUTLAW level.
My tips are:
- Try to get one or two stars in all the races, don't re-do them even though you think you might get a little bit better. (I tried one of the speed trap races like 20 times but all I could get was 2 stars. Then with a better car it was a piece of cake)
- Always use a new car as soon as you unlock it. New cars are usually better - improved speed, acceleration or handling.
- Re-do the races that you're good at to get more bounty (XP). A race you've already done will give you less bounty though. So re-doing races you only get one star in won't get you very far. New races are always better.
- With a good car you can afford a few mistakes and still ace the race.