Drive faster:
Press Right Analog-stick Up to crouch down and drive faster.
Extra points:
Combine flips with spins after a jump or land on only two wheels for extra points.
Fun meter:
The Fun meter controls how well you can do stunts. To increase it, do more stunts.
Karma meter:
The Karma meter keeps opponents from hitting back after you hit them. To increase it, always press X to apologize to racers on your team after you accidentally hit them. Doing this a lot will decrease its value.
Speed meter:
The Speed meter controls how fast your kart can race. To increase it, drive at full speed and make large come-backs.