For the snowboarding you want to take the corners with as little space between you and the walls as possible. Also add in the fact your trying to get the most boosts you can out of every turn and you've got yourself a really good time. A little trick you can use is on the striaghts pick tails and quicly move from side to side skidding, getting boosts all the time. also boosting right before a jump gives huge speed and distance, experimate with this for every jump, see what works.