Use the Turbo Boost function as much as possible.
Remember that the Boost is replenished over time
(as seen on the Boost meter within the revs counter).
Boost increases speed, but also increases turning ability for sharp corners
Learn the tracks. This way you'll know which gates can be skipped for maximum advantage.
Maintaining high speed is more important that sticking to the racing line.
If you need to make a sharp turn very quickly, apply reverse thrust and
opposite lock on the steering. This manouevre loses some speed and is hard to master, but can be very useful in tight spots.
Learn the strengths and weaknesses of the individual champs, so you can use the best racer for each track.
Take care to avoid other competitors - a bad collision can seriously slow you down and send you off course.