Use inward drifting bikes (ex: Bullet Bike, Mach Bike, Flame Runner)
Hold down the accelerator as "2" is starting to disappear on "3", "2", "1", "GO!" to get a rocket start in this game and then wheelie.
Don't turn with just the control stick.
Turn with the control stick while in a drift.
Use mini turbos and wheelies to transition from turns to straight aways (release the drift button once sparks are on the tires).
Wheelie on all straight aways.
Start with working on turning with inward drifting bikes.
Most people who start drifting on turns hit the drift button and turn at the same time. There are a few turns where this is faster, but generally...
You want to hit the drift button and then start turning right before the vehicle's hop animation ends. This is called a delayed drift.
Delayed drifts allow you to have an easier time building mini turbos on turns.
After building mini turbos from these delayed drifts, adjust your line and then wheelie before the mini turbo ends (the earlier you get the wheelie out the better). This action keeps you at top speed.
After being in a wheelie at top speed, try not to turn in the wheelie at all to keep your top speed.
Rinse and repeat.
If you are hit by an item and slow down a lot, hold down the accelerator and brake/drift button at the same time, then release and wheelie.
Those are the basics, and they are essential to get down first.