Do barrel rolls and get as much air time as possible. You can increase your time in the air by using the nitro just before getting on a platform.
Drifting
Drift around corners to avoid slowing down too much.
Nitro
Nitro boosts your speed. Try to it whenever possible and save it until you can use it to its full potential, as in straight-aways. If you have a nitro at the end of the race, use it then to maintain or get the lead.
Upgrades
Save money to purchase upgrades. Get the Handling upgrade first to increase control. Then purchase the Top Speed is a must, followed by Nitro and Acceleration.