Easy wins
In races where crew members are used, use a scout (Yumi if possible). If you do not win the race, your scout usually will.
In Career mode, choose the Exotic class. When you get to the Stacked Deck level, get a Chevrolet Corvette Z06. Neville, Colin, and Nikki should still have exotic cars. Choose one of them and do any race where you can use your wingman. You should get an easy win.
For easier Speedtrap races, activate your Blocker/Brawler before the race. While racing and you are coming up to a speed trap, stop your Blocker/Brawler. This will crash the other car(s), and drastically slow down their time. Remember that the peak Blocker/Brawler moment is just before the speed trap.
When in a Speedtrap race, use a drafter (Niki if possible). When you get close to a speedtrap, activate your crew member and draft.
When in Career mode, choose the Exotic class. When you get to the Stacked Deck level, get a Chevrolet Corvette Z06. Once this happens, Neville, Colin, and Nikki will still have exotic cars. Choose one of them and do any race where you can use your wingman. You should have easy win.
When you get to the Stacked Deck level and go to do the canyon race for a Lamborghini Murcielago, use a Corvette Z06 stock/custom to overtake him.
The easiest way to win Circuit Races, Sprints, Rival Crew Challenges,Checkpoints, Speedtrap or any other race where nitrous and SpeedBreaker are allowed is by enabling the "Unlimited nitrous" and "Unlimited SpeedBreaker" codes. Use them at the same time throughout the entire race. This will let you make sharp turns and drive fast with control to get ahead of your opponents or maintain speed in the Speed Trap races.
While in the Canyon race you will see that there are areas marked with white lines with stripes on the side of the roads near the big turns. If you follow those lines you will have the shortest turn and thus be able to win the race easily.
Enable the "Unlimited nitrous" and "Unlimited crew charge" codes. Activate your drafter (if in the crew). Keep the drafter activated from the start of the race. Follow him or her and you or your drafter will certainly win the race.
Enable the "Unlimited nitrous" and "Unlimited SpeedBreaker" codes. During the race, keep using SpeedBreaker until the end. Also use nitrous through the entire race. This will make it an unfair slow motion race, that is painfully long but a sure win. To boost the effects, enable the "Unlimited crew charge" code as well and have a drafter as active. Then use your drafter during the entire race. It is faster, but still painfully long. Note: This cannot be used in Quick Race, Challenge Series or Canyon Duels.
For easy wins at the canyon, use the following cars. Tuner: Nissan 350z or Skyline R34; Exotic: Porsche Carrera GT or Lamborghini Muricielago; or Muscle: Dodge Viper SRT10 or Dodge Challenger R/T.