Halfpipe
Here is some stuff that will help you score good in the halfpipe
Halfpipe start bonus
At the start of the halfpipe, immediately turn to the left or right. Proceed until you are near the wall, then make a turn towards the pipe. If you are in the correct position, you will move up a small invisible ramp and it will boost you high into the air. The best part of this glitch is that you land every trick, no matter how bad your landing position is (exception: not letting go on a grab). Can you say '13000 combo bonus'?
Easy Landings
Here's a trick that will help you nail every landing. In the air, line your board up with the groung, maybe leaning back a little bit and right before you hit the ground, press Z. If you did it right your legs will come up right before you hit the ground and you'll have a MUCH smoother landing.
When you get to the shorter hill before the finish, use your jump button and try a big combo. Don't worry about landing because when you cross the line you'll land automaticly. This will allow you to get extra points at the end.