Make minor adjustments while changing directions. Turning too quickly decreases your speed rapidly.
When there is incoming traffic, try to push your opponents into it causing them to have an accident. This will get you a lot of valuable time.
Save nitrous for the last lap, because no matter how good your lead, the comp always manages to catch up to you on the last lap (if catch-up option is enabled) especially at higher difficulties.
Don't stay near the centre of the road if it will force you to go slow. Use the entire width of the track to get you a faster lap.
If you are having problems avoiding traffic, use a car with great handling even if it means compromising slightly on top speed.
Keep one eye on the minimap. Always know the direction and how sharp the next few corners are.
The camera view that you select is very important. Never ever select the in-car view as it eats up a significant portion of the display and blocks a huge part of the track from view.
Make sure you have a good FPS (atleast 40). A smoothly running game does affect how well you drive. If the game stutters at a crucial time, it could ruin your entire race.