100m Freestyle
To become first in basicly every time you play, use Sonic or Shadow in my view. They have very basic shapes. (Not like Blaze with the figure of 8) Sonic is the Left to Right shape. Rub really fast like in the running. Shadow is up and down. That's not hard. Just turn the Nintendo DS so it's left to right. Rub really fast etc.

10m Platform
This is quite hard for some people but for me its really easy. To get max height when jumping off the board, press and hold down 'A' for about 2 seconds then release. As soon as the button prompts come up, don't bother looking to see which one is 'A' and which one is 'B'. Just focus on the screen and make it so your right hand presses the very right button first then the bottom one and repeat till you have done all the prompts. Do this for each set of prompts. Just memorise where each button is.
X
Y A
B
Then when you have to press 'A' at the right timing to do a perfect dive, focus on the screen and when your character is about facing downward, press the very right button to do a perfect dive at about 00.02 Degrees. Using this tip/cheat/hint/help you should be getting almost perfect 10's or 9.50's