From StrategyWiki, the free strategy guide and walkthrough wiki

• : Turn the kart.
• : Accelerate.
• : Brake.
  • +: Accelerate in reverse.
• : Drift to the left.
• : Drift to the right.
• : Swap drivers.
• /: Use item.
• : Pause a race or battle.
• Tip: While drifting, repeatedly move the joystick left and right to build up a mini boost. (You will see the Kart exhaust change color) Stop drifting to activate the boost.